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Article

Integrated Documentation and Non-Destructive Surface Characterization of Ancient Egyptian Sandstone Blocks at Karnak Temples (Luxor, Egypt)

by
Abdelrhman Fahmy
1,2,3,*,
Salvador Domínguez-Bella
3,4,5,
Ana Durante-Macías
3,
Fabiola Martínez-Viñas
6 and
Eduardo Molina-Piernas
3,4,5,*
1
Conservation Department, Faculty of Archaeology, Cairo University, Giza 12613, Egypt
2
Rathgen Research Laboratory, National Museums of Berlin, Schloßstraße 1A, 14059 Berlin, Germany
3
UGEA-PHAM, Faculty of Sciences, University of Cádiz, Campus Rio San Pedro, 11519 Puerto Real, Cádiz, Spain
4
Department of Earth Sciences, Faculty of Sciences, University of Cádiz, Campus Rio San Pedro, 11519 Puerto Real, Cádiz, Spain
5
Instituto Universitario de Investigación Marina (INMAR), University of Cádiz, Campus Rio San Pedro, 11519 Puerto Real, Cádiz, Spain
6
Independent Researcher, 11130 Chiclana de la Frontera, Cádiz, Spain
*
Authors to whom correspondence should be addressed.
Heritage 2025, 8(8), 320; https://doi.org/10.3390/heritage8080320
Submission received: 3 July 2025 / Revised: 4 August 2025 / Accepted: 8 August 2025 / Published: 11 August 2025
(This article belongs to the Section Materials and Heritage)
Browse Figures
Versions Notes

Abstract

The Karnak Temples are considered one of Egypt’s most significant archaeological sites, dating back to the Middle Kingdom (c. 2000–1700 BC) and were continuously expanded until the Ptolemaic period (305–30 BC). As the second most visited UNESCO World Heritage archaeological site in Egypt after the Giza Pyramids, Karnak faces severe deterioration processes due to prolonged exposure to environmental impacts, mechanical damage, and historical interventions. This study employs a multidisciplinary approach integrating non-destructive testing (NDT) methods to assess the physical and mechanical condition and degradation mechanisms of scattered sandstone blocks at the site. Advanced documentation techniques, including Reflectance Transformation Imaging (RTI), photogrammetry, and Infrared Thermography (IRT), were used to analyze surface morphology, thermal stress effects, and weathering patterns. Ultrasonic Pulse Velocity (UPV) testing provided internal structural assessments, while spectral and gloss analysis quantified chromatic alterations and surface roughness. Additionally, the Karsten Tube test determined the water absorption behavior of the sandstone, highlighting variations in porosity and susceptibility to salt crystallization. In this sense, the results indicate that climatic factors such as extreme temperature fluctuations, wind erosion, and groundwater infiltration contributed to sandstone deterioration. Thermal cycling leads to microcracking and granular disintegration, while high capillary water absorption accelerates chemical weathering processes. UPV analyses showed substantial internal decay, with low-velocity zones correlating with fractures and differential cementation loss. Finally, an interventive conservation plan was proposed.

1. Introduction

The preservation of stone monuments is considered a multifaceted challenge that requires balancing historical conservation with scientific inquiry. Stone monuments are susceptible to various forms of deterioration, including weathering, biological growth, structural instability, and human-induced damage. In addition, understanding the state of preservation and diagnosing structural issues without compromising the monument’s durability is essential. Buildings and architectural elements serve as ancient structures and irreplaceable records of human history and artistry. These structures were often made with natural stones, each with distinct physical and chemical properties that influence how they respond to environmental factors [1,2,3]. Exposure to factors like moisture, salt crystallization, thermal expansion, pollution, and biological colonization results in material decay over time [4,5,6]. In this context, assessing the extent of this decay is essential for planning effective conservation strategies, but invasive methods, such as coring or drilling, risk further damage to fragile stone surfaces. For that, NDT techniques offer an alternative and supporting role, enabling in-depth structural and material analysis without destructive intervention [7,8]. In this sense, non-destructive testing (NDT) has emerged as a key methodology for heritage conservation, allowing researchers and conservators to investigate material properties, detect subsurface anomalies, and monitor degradation processes without physically altering or damaging the monument [7,9].
Photogrammetry and Reflectance Transformation Imaging (RTI) are advanced documentation techniques that have been utilized in many studies for archaeological recording. In this sense, photogrammetry is a 3D reconstruction technique based on the principle of deriving spatial measurements and models from overlapping two-dimensional images. It enables the creation of accurate, scaled digital models of objects and surfaces by using computational algorithms to triangulate image data. In the field of cultural heritage, photogrammetry has proven particularly effective for documenting monuments, sculptures, and stone blocks, capturing intricate surface details and enabling long-term condition monitoring and comparative analysis [10]. Reflectance Transformation Imaging (RTI), also known as Polynomial Texture Mapping (PTM), is a computational photographic method that captures the surface shape and texture of an object under varying lighting conditions. By allowing interactive re-lighting, RTI reveals subtle surface variations, inscriptions, and tool marks that are often invisible under static lighting. It has become an essential tool in heritage conservation, particularly for the detailed examination of weathering phenomena, surface erosion, and microtopographic features [11]. Together, these techniques provide complementary datasets for comprehensive surface analysis. While photogrammetry offers geometric and spatial accuracy for three-dimensional modeling, RTI enhances the visualization of fine surface features critical for diagnostic conservation work. For this, their integration has enriched documentation standards and condition assessments in archaeological and architectural heritage research and serves as a reliable, non-invasive tool for establishing baseline records, which can later be compared to future datasets to assess the rate and extent of material change [12]. For physical and mechanical assessment, NDT encompasses a variety of techniques that collectively provide a comprehensive view of a stone monument’s condition. Each technique detects and characterizes different aspects of the stone’s structure to allow us to gather comprehensive data that informs conservation decisions [13,14]. For instance, ultrasonic pulse velocity testing measures the velocity of ultrasonic waves traveling through stone, with wave speed variations indicating internal flaws such as cracks, voids, differential weathering detection, and density changes, making it a reliable technique for structural assessment [15]. In addition, infrared thermography captures thermal images that reveal temperature variations on stone surfaces, which can be indicative of moisture ingress, delamination, or internal voids. For this sense and by analyzing thermal patterns, conservators can identify and monitor areas of decay that may require treatment and intervention [16,17]. Glossmetry measures surface reflectivity, while colorimetry assesses color stability and variations. These complementary techniques help monitor surface degradation, pigment loss, and chemical changes, guiding conservation treatments to preserve the aesthetic and archaeological fabric, and help in assessing the conservation material’s effectiveness [18,19]. Karsten Tube test is a widely used non-destructive technique for evaluating the water absorption properties of stone and other porous materials. This method involves attaching a glass or plastic tube filled with water to the stone surface using a sealing compound, allowing researchers to measure the rate at which water is absorbed over time. In this regard, the test provides information about the stone’s porosity, permeability, and susceptibility to weathering, which are important factors in conservation and restoration efforts [20,21]. In addition, Karsten Tube test helps conservators’ understanding of sensitivity to present climatic cycles, making it an essential non-invasive tool in heritage preservation and construction diagnostics [22].
The current study aims to employ and validate various non-destructive testing (NDT) methods for the condition assessment of ancient Egyptian stone blocks at Karnak Temples. The construction at Karnak Temples began during the reign of Senusret I (1971–1926 BC) in the Middle Kingdom (c. 2000–1700 BC) and continued into the Ptolemaic Kingdom (305–30 BC), although most of the existing structures date from the New Kingdom [23,24]. Throughout the Karnak Temples, thousands of scattered stone blocks are in a poor state of conservation (Figure 1A). Local environmental conditions have significantly impacted the durability of these stones [25]. The primary factors contributing to their decay include thermal expansion and contraction due to heat and cool cycles, wind erosion, and groundwater infiltration. In this context, these factors lead to both mechanical and chemical deterioration of the stone material. To address these challenges, the archaeological mission of the University of Cádiz (Karnak Stones Project (KSP), concession 2024 https://karnakstonesproject.com/) at Karnak Temples aims to preserve these scattered blocks (Figure 1B). To achieve this, a series of field observations, assessments, and monitoring activities have been conducted using multiple documentation and physical, mechanical, and non-destructive techniques to assess the physical and mechanical condition, document, and evaluate the quality of the sandstone blocks for future conservation purposes.

2. Methodology

The documentation and analysis of the sandstone blocks in the three Mastabas at the northeastern area of Karnak Temples followed a multidisciplinary approach, combining traditional archaeological practices with advanced digital technologies. The process began with a thorough site survey and geolocation mapping to accurately position each block within the site plan. This spatial data was integrated with photogrammetry and RTI to generate high-resolution digital models, allowing for detailed morphological analysis and for future virtual reconstruction. In the current research, representative sandstone blocks were selected from the three Mastabas carrying codes of M1-3615, M1-3577, M2-3502, and M3-3553 for their priorities of conservation and decay state. For each selected block, measurements were recorded using digital calipers and laser distance meters to ensure dimensional accuracy.
Reflectance Transformation Imaging (RTI) is an important non-destructive technique for documentation and high-resolution surface analysis in archaeological and conservation studies [26,27,28]. In the 2024 season, the highlight RTI (H-RTI) [27] method was employed to enhance the visualization of eroded inscriptions, tool marks, and microstructural anomalies. A Nikon D810 (manufactured by Nikon Corporation, Tokyo, Japan) with a light-diffusing system was tripod-mounted, while black spheres stabilized on separate tripods ensured precise reflectance modeling. A standardized imaging protocol captured approximately 25 raw-format images at varying light angles (20–30% overlap), processed via RTIBuilder (v.2.0.2) for polynomial texture mapping (PTM). RTIViewer (v.1.1.0) analysis enabled advanced morphological assessments, facilitating conservation diagnostics and condition monitoring.
Photogrammetry for 3D modeling was conducted using a structured methodology to ensure high accuracy and detailed documentation of the selected sandstone blocks. The process began with systematic image capture utilizing high-resolution digital cameras with fixed focal lengths to minimize distortion, overlapping 60–80% to facilitate accurate 3D reconstruction. Furthermore, the captured images were then processed using photogrammetry software, which aligned the photos, generated point clouds, and constructed detailed 3D models.
Chromatic and surface alterations in weathered stones provide important information about environmental and weathering dynamics [29,30]. For that, a portable spectrophotometer CM2600d (manufactured by Konica Minolta, Tokyo, Japan) was employed to assess spectral properties via the SCE (specular component excluded) method. The CIELab* color space (L*, a*, and b*) and SCE method were selected because they specifically exclude the specular (glossy, mirror-like) reflection, meaning they measure only the light that has penetrated the surface and been diffusely reflected by the colorants within the sandstone itself. Additionally, a Rhopoint glossmeter (manufactured by Rhopoint Instruments, Sussex, United Kingdom) quantified surface reflectivity, with gloss variations serving as indicators of microstructural alterations induced by weathering, chemical interactions, and environmental impact [31].
Infrared thermography was carried out to capture temperature variations across the surface stone that can detect moisture distribution, structural problems, and material degradation. A FLIR C5 (manufactured by Teledyne FLIR, Wilsonville, OR, USA) thermal camera was used with a resolution of 160 × 120 pixels and MSX® (Multi-Spectral Dynamic Imaging) mode. The temperature range of the device extended from −20 °C to +400 °C, with a precision of ±2 °C, allowing for accurate detection of temperature variations. It is important to note that the current thermographic survey was conducted using passive infrared thermography, which measures the natural thermal emission from the stone surfaces under varying environmental conditions. While this approach provided a useful preliminary understanding of surface temperature distribution and diurnal thermal gradients, it does not allow for the detection of subsurface defects or internal structural anomalies. Therefore, the data should be interpreted primarily as indicators of surface-level thermal behavior and potential stress points rather than definitive evidence of internal deterioration.
To assess the water absorption properties of the sandstone blocks, two Karsten Tube penetration tests were conducted on four selected sandstone blocks. The tests were performed at two different spots on each block to ensure consistency and reliability of the results. The blocks were carefully prepared by removing any surface dust or dirt to ensure that the absorption measurements reflected the material’s intrinsic properties. In this sense, water was then introduced into the Karsten Tubes, and the rate at which it was absorbed by the sandstone was monitored over a specified time. The water absorption coefficients and rates were calculated by analyzing the volume of water absorbed over time, following standard procedures. Water absorption coefficient (WC) was calculated according to [32]:
WC = V/(A × √t)
where “Wc” is the water absorption coefficient (kg/m2√s), “V” is the volume of absorbed water (ml) convert to kg, “A” is the area of the tested surface (m2) considering a diameter “d” equal to 0.05 m and, “t” is the time (seconds). In addition, water absorption rate “W” was calculated and refers to how much water the stone absorbed per second, and it is a simple measure of the absorption speed and calculated according to the following formula:
ΔW = V/t
where “W” is the water absorption coefficient (mL/s), “V” is the volume of water absorbed (mL), and “t” is the time (seconds).
The Ultrasonic Pulse Velocity (UPV) test is an effective method to evaluate the structural consistency and quality of stone monuments [33,34]. UPV works by transmitting ultrasonic pulses through a material and measuring the time taken for the waves to travel from a transmitter (T) to a receiver (R) [35]. In the current study, a portable tester device model 58-E4800 (CONTROLS Cernusco, Gessate, Italy), equipped with a standard probe operating at 54 KHz, was used [36]. Field testing often adheres to established standards ISO 16823:2025 [37] to ensure consistency and reliability in data collection and interpretation. In fieldwork, grids were planned to cover multiple points systematically, with the distance between the transmitter and receiver typically set at 10 cm and 15 cm for indirect and semidirect measurements. To determine the pulse velocity values (V), a straightforward relationship between the distance travelled by ultrasonic waves and the time taken for their propagation is utilized. In addition, the degree of anisotropy is quantified using the formula for the Anisotropy (%) = UPVmax − UPVmin/ UPVmax × 100.

3. Results

3.1. Planimetry and On-Site Observation

A comprehensive general plan and geolocation of the blocks in the three mastabas within the northeastern area of Karnak Temples have been conducted for all blocks in Mastaba 1, 2, and 3 (labeled as M1, M2, and M3, respectively). In this sense, it is observed that most of the blocks had been previously numbered and organized using copper plates by French archaeologists over 50 years ago. However, it was observed that some blocks lacked the French numbering. To address this, the Spanish-Egyptian mission assigned a new identifier to the unnumbered blocks, using the UCA (University of Cádiz) coding system (Figure 2). In addition, on Mastaba 1, a total of 80 blocks were previously numbered by the French system, while 21 blocks were unnumbered and were digitally coded by the current mission as UCA1 to UCA21. In Mastaba 2, 55 blocks carried French numbers and 3 unnumbered blocks, receiving UCA designations. Similarly, in Mastaba 3, 42 blocks had French numbers and 1 unnumbered and newly introduced UCA codes. In this sense, all blocks are now traceable, facilitating future conservation, analysis, and archeological interpretations. The currently studied blocks in the article have been highlighted, with their precise locations and numbers documented and photographs (Figure 2) and their main characteristics are summarized in Table 1. Detailed measurements and observations were collected, providing valuable information for each block’s archeological and material context.
In Mastaba 1, Block ID 3615 (Figure 2), a sandstone block from the reign of King Seti I (19th Dynasty, New Kingdom), measures 100 × 120 × 60 cm. The stone is creamy in color, with fine, compact grains and a parallelepiped shape. The upper surface is flattened by chiseling, with coarse quarry keying on the sides and finer keying marks at the back. A hole on the upper face likely facilitated block joining, while the front face features detailed reliefs of the city of Behdet (a wheel) and wings, partially covered with crust and traces of Egyptian blue pigment over mortar-filled cavities. Another block with ID 3577 (Figure 2), in the same mastaba and sector, measures 160 × 75 × 40 cm and bears inscriptions, though erosion and cracking along lamination planes threaten their preservation. Its creamy, homogenous texture exhibits altered yellowish levels and prominent cross lamination, with a 12 mm-wide keying mark on the upper face, emphasizing the need for careful conservation. In Mastaba 2, Block ID 3502-30 (Figure 2), a perfectly cylindrical sandstone block from King Seti I’s reign measures 90 cm in height, with a diameter of 2.20 m and a radius of 1.10 m. The block’s finely finished upper part displays 20 mm chisel strokes, holes, and dovetail joints, while the back-diagonal plane retains traces of white mortar. In addition, well-preserved hieroglyphic reliefs and pharaoh’s cartouches adorn the lower zone, though no remnants of polychrome surfaces were found. Finally, in Mastaba 3, Block ID 3553-46 (Figure 2), measuring 145 × 85 × 65 cm, features high-relief carvings of a sun symbol, a central vulture, and Seti I’s cartouches, with an inscription referencing “Skhet 3at Mret Ptah.” The inverted block shows irregular fractures, upper surface deterioration, and evidence of biofilm growth and salt efflorescence, though its carvings remain archeologically important.

3.2. Reflectance Transformation Imaging (RTI)

Figure 3 presents Reflectance Transformation Imaging (RTI) visualizations of the four inscribed sandstone blocks from Karnak, using a combination of specular enhancement, polynomial texture mapping (PTM), and close-up renderings to reveal surface details. The block M1-3615 displays relatively well-preserved hieroglyphs, though erosion, surface delamination, and minor cracking are evident. Specular lighting emphasizes tool marks and carved reliefs, while PTM highlights depth variations, aiding in assessing weathering patterns and the original carving techniques (Figure 3). In addition, the block M1-3577 focuses on a decorated block with a winged motif and circular symbols. RTI reveals surface pitting, abrasions, and remnants of Egyptian blue pigment. Differences in wear and tool traces reflect both environmental degradation and reuse. Close-ups expose microfractures and small-scale flaking along edges and carved lines (Figure 3). Furthermore, in the block M2-3502, inscriptions appear crisp in some areas and deteriorated in others, especially near the base, where granular disintegration and erosion have led to material loss. Enhanced lighting shows fine incisions, surface irregularities, and evidence of past mechanical damage (Figure 3). Finally, the block M3-3553 captures a fragment with visible inscriptions and iconography. In this sense, RTI demonstrates erosion in lower sections, with normal and raking light views enhancing the readability of shallow carvings. Micro-topographic mapping highlights subtle relief features, scratches, and ancient tool marks (Figure 3).

3.3. Photogrammetry

Photogrammetry allows for the precise digital reconstruction and documentation of the analyzed blocks. In this sense, Figure 4 displays multiple perspectives for each block to enable a comprehensive analysis of their physical condition, inscriptions, and archeological significance. The use of 3D modeling enhances the study of these blocks by capturing fine details such as inscriptions, tool marks, and weathering patterns that may not be easily visible in traditional documentation methods. In this regard, the block M1-3615 is considered a fragment of a larger architectural element, possibly from a column or wall in the Karnak Temples (Figure 4). The visible striations and weathering patterns reflect extensive exposure to environmental elements, and the absence of inscriptions indicates a high weathering rate of this block. Conservation concerns for this block include surface delamination and moisture/thermal-related degradation. In addition, black deposits observed on the lower part are due to prolonged exposure to humidity, which necessitates intervention to prevent further damage.
The block M1-3577 contains visible horizontal lines, and it is part of an inscribed wall or architectural frieze in Karnak (Figure 4). The presence of hieroglyphs and remains of pigments such as Egyptian blue confirms its archaeological and epigraphic importance. In the block M1-3615, the side of the block displays a rough texture for quarrying marks and may be reused in later periods. From a conservation standpoint, this block exhibits significant surface erosion affecting the clarity of some inscriptions. The edges are fragile, increasing the risk of further fragmentation, while discoloration and mineral deposits indicate ongoing chemical weathering due to environmental conditions and the way of preservation (Figure 4). Furthermore, the block M2-3502 is considered a cylindrical section of a column from a damaged column in the hypostyle hall of Karnak Temples (Figure 4). The inscriptions on its surface remain relatively well-preserved. However, visible cracks and fractures indicate structural weaknesses that require structural rejoining. The surface inscriptions also show signs of weathering, disintegration, and material loss in the lower parts caused by handling, erosion, or maybe past restoration attempts and displacement. Finally, the block M3-3553 is considered a fragment of a larger architectural element from a wall in the Karnak context (Figure 4). In terms of conservation, the edges are chipped, and the corners display significant wear due to a high risk of mechanical damage. Some areas exhibit surface encrustations that could be caused by salt crystallization or prolonged exposure to environmental conditions.

3.4. Spectral and Gloss Analysis

The spectral and gloss analysis of sandstone in block M1-3615 demonstrates variations in surface condition Table 2 and (Figure 5, for spatial distribution of measured points). The lightness (L*) values range from 57.69 to 70.17, which indicates areas of darker discoloration due to soiling and moisture, while lighter sections refer to surface erosion or material loss. The color metrics (a*, b*, Hue, Chroma) show warm, earthy tones typical of sandstone, but the variation in chroma (11.75–18.99) could reflect mineralogical changes due to decay. The gloss values (0.5–2.5%) are consistently low, which reflects a rough and weathered surface. The spectral and gloss analysis of sandstone in block M1-3577 indicates significant surface variability (Table 2 and Figure 5) for the spatial distribution of measured points. Lightness (L*) values range from 43.03 to 60.84 in darker areas and which could be linked to heavy soiling, biological growth, and moisture infiltration, while lighter sections are connected to less weathered surfaces. The color metrics show warm hues with relatively high chroma values (17.36–21.32), showing that some areas retain stronger pigmentation and discoloration. Notably, the third measurement shows an unusually high chroma (81.34), which indicates a distinct pigment concentration and mineral deposit. Gloss values (1.5–4.2%) remain low, highlighting a rough and weathered surface with areas of varying reflectivity due to surface irregularities and decay.
In sandstone block M2-3502, L* values (brightness) range from 54.28 to 63.15, with lower values reflecting a bit of darkening due to surface soiling (Table 2 and Figure 5, for spatial distribution of measured points). In addition, the a* and b* values (color components) show moderate red and yellow hues, with slight variations in chroma (color intensity) caused by iron oxide staining of the sandstone. The gloss (GU%) is very low (0.8–1.8), indicating a rough and weathered surface with minimal reflectivity, possibly due to granular disintegration and surface micro-cracking. Finally, Table 2 shows the decrease of L* values (63.15 to 54.28), which indicates darkening due to soiling, biological growth, and mineralogical changes in the sandstone block M2-3502. Variations in a* and b* values reflect iron oxide staining impact with shifts in hue and chroma that point to differential weathering. The extremely low gloss (0.8–1.8 GU) indicates a rough and matte surface, likely caused by granular disintegration, micro-cracking, and surface degradation of the stone.

3.5. Infrared Thermographic Survey (IRT)

The thermographic analysis across the sandstone blocks under different exposures (morning, midday, and afternoon) (Figure 6 and Figure 7) presents the temperature fluctuations throughout the day, with temperatures peaking around 60.6 °C at 3:30 p.m., dropping to around 34.8 °C by 8:30 a.m., and reaching their lowest at around 22.1 °C in the early morning (6:30 a.m.). Thermal images show a gradual increase in surface temperature with the highest heat accumulation on the block surfaces, especially in areas exposed to direct sunlight. The color spectrum shifts from deep purple (low heat) in the morning to bright yellow and orange (high heat) as the day progresses due to the substantial thermal stress. This thermal cycle induces micro-expansion and contraction within the stone matrix. The sandstone’s porosity exacerbates this effect, as water or moisture within the pores evaporates rapidly under high temperatures, creating pressure that weakens the stone’s internal structure. The repeated expansion and contraction cause microcracks, which progressively widen and lead to surface exfoliation, granular disintegration, and even block delamination. The thermal stress directly correlates with common sandstone decay patterns observed on-site, including scaling, powdering, sanding, and crust formation. The presence of salts in the sandstone can intensify damage through salt crystallization, during temperature spikes, moisture carrying dissolved salts rises to the surface, and upon cooling, the salts recrystallize, exerting pressure that fractures the stone [6]. The decay is most pronounced on the block surfaces facing prolonged sun exposure, as shown by the thermal gradients in the images. Additionally, the sharp temperature drop at night induces thermal shock, accelerating stone fatigue and structural instability. In this context, Shen et al. [38] explained that sandstone exposed to high levels of heating causes internal microstructure and produces various intergranular cracks around the quartz crystals, ending with full decomposition. Furthermore, Lü et al. [39] demonstrated that high temperature affects the physical and mechanical characteristics of the sandstone, causing irreparable loss of the material fabric.
Although direct mechanical testing of the blocks was not possible due to preservation constraints, the influence of thermal stress remains a relevant consideration in understanding their long-term degradation. Quartz-rich sandstones, such as those observed in the studied blocks, typically exhibit a coefficient of thermal expansion (α) in the range of 8 to 12 × 10−6 °C−1, and an elastic modulus (E) between 10 and 30 GPa, depending on grain size, porosity, and cementation quality [40,41,42,43]. Under daily temperature variations that can exceed 40 °C in Upper Egypt, these properties indicate that internal dimensional fluctuations and thermally induced stresses are likely to occur, particularly in structurally heterogeneous or weathered zones. While this analysis is theoretical in the absence of direct mechanical testing, it aligns with our observations of microcracking, surface delamination, and anisotropic ultrasonic velocity distribution.

3.6. Surface Hydric Behavior

The water absorption coefficient parameters (Wc) and water absorption rates (W) measured through the Karsten tube penetration test provided important insights into the porosity and capillary water transport properties of the sandstone blocks. The results show differences across the studied blocks, reflecting variations in stone density, pore structure, and prior weathering effects. For instance, block M1-3615 displayed the highest Wc value (0.031 kg/m2s) and a corresponding high W value (0.5 mL/s) (Figure 8), which reflects high capillary water uptake. This interprets a more open pore network that can accelerate decay through salt crystallization and heat-cool cycles. In contrast, block M1-3577 exhibited lower absorption values (Wc = 0.018 kg/m2s, W = 0.1 mL/s), pointing to reduced porosity or partial pore clogging. This lower absorption might slow down water-induced decay but could trap salts within the stone, leading to sub-surface damage. Block M2-3502 had similar high-water absorption rates (Wc = 0.031 kg/m2s, W = 0.5 mL/s) as block M1-3615, indicating susceptibility to water ingress, which aligns with the visual observations of block degradation. In addition, the blocks from Mastaba 3 (M3-3553) had the lowest values (Wc = 0.006 kg/m2s, W = 0.03 mL/s), implying minimal water penetration and reflecting a bit high cemented area. While lower water uptake might seem protective, it can also reduce the stone’s ability to dry out, prolonging internal moisture exposure. In this context, the test results correspond with the material characteristics observed during site observation for blocks that have quartz-dominated structures, heavy minerals, and occasional muscovite laminas. In addition, sandstones with higher water absorption rates are likely more vulnerable to mechanical stress and chemical weathering, especially in Luxor’s environment with extreme temperatures.

3.7. Ultrasonic Pulse Velocity (UPV)

In Figure 9B,D,F,H), ultrasonic pulse velocity (UPV) results are visualized as heatmaps that correspond to specific transmission paths measured across the sandstone blocks (Table 3). These paths were acquired through both direct and semidirect ultrasonic measurements, systematically performed and illustrated in the corresponding setup diagrams (Figure 9A,C,E,G). For the block M1-3615 (Figure 9A,B), the paths labeled with reversed or crossing numbers (e.g., 1-12, 2-11) represent semidirect measurements, capturing internal stone characteristics across opposing surfaces. In contrast, the groups labeled as L1 (e.g., 7–8 to 11–12), L2 (e.g., 13–14 to 18–19), and L3 (e.g., 20–21 to 25–26) reflect direct transmission paths aligned along three successive horizontal rows, allowing for a stratified assessment of internal consistency across the block’s thickness.
In the block M1-3577 (Figure 9C,D), ultrasonic measurements were carried out along three horizontal lines designated as L1 (1–2 to 4–5), L2 (6–7 to 9–10), and L3 (11–12 to 14–15), all corresponding to direct paths. These horizontal sequences provide uniformity and structural soundness of the block along distinct elevations. Additionally, semidirect measurements were taken at corner points such as 1–2 and 3–4 to allow for comparative analysis between lateral and depth-directed acoustic propagation. For block M2-3502 (Figure 9E,F), the upper corner points, labeled 1–1 through 4–4, were tested using semidirect transmission, providing vertical penetration data, important for understanding stone coherence at the edges. Conversely, the paths from 5–6 to 13–14 focus on an area with a visible structural crack and were measured using direct paths, enabling targeted analysis of deterioration localized around the defect zone.
In block M3-3553 (Figure 9G,H), the semidirect measurements were again focused on the northeastern corner, involving paths 1–1 to 4–4. Two vertical columns of direct measurements, labeled L1 (1–5 to 8–9) and L2 (2–10 to 13–14), were conducted to capture vertical structural variations. In addition, a series of direct measurements crossing the visibly fractured area, ranging from 1–2 to 9–14, were carried out to evaluate the severity and extent of internal damage caused by cracking and differential weathering.
The ultrasonic results show a distinct distribution of pulse velocities within the studied sandstone blocks in M1, M2, and M3 (Figure 8) and Table 3. High-velocity zones, which are indicated in yellow and green, correspond to areas of greater material coherence, where the stone’s internal structure remains dense and well-consolidated. In these regions, the tightly packed quartz grains and intact cementing material allow sound waves to travel quickly with minimal scattering. Conversely, low-velocity areas, shown in purple and blue, signify regions of internal decay. Healthy sandstone typically shows ultrasonic pulse velocity (UPV) readings above 2.0 km/s and often ranges between 2.2–2.8 km/s depending on the mineral composition and cementation quality. In contrast, the results from the studied blocks showed lower velocities that highlight varying degrees of weathering and internal damage. The high-velocity zones with readings between 1.5–2.0 km/s reflect areas where the stone retains relatively good fabric, though still below pristine sandstone values (Figure 8). These regions might represent more cohesive quartz aggregates with less porosity, but the velocity drop below 2 km/s already indicates partial weathering, microcracks, and/or natural internal anisotropies of the rock, such as laminations, clast orientation, and a greater number of pores (Figure 9). In the deteriorated zones, velocities drop drastically, reaching values as low as 0.2–0.8 km/s. These low-velocity areas correspond to sections with visible fractures, laminations, and internal voids, where sound waves are severely attenuated or reflected (Figure 9A,E,G). The strong contrast with healthy sandstone refers to the extent of decay. For instance, the laminated sections show velocities around 0.6 km/s that indicate high material weakening compared to the value 2.5 km/s of healthy measured sandstone, showing some areas with local velocity spikes up to 2.0 km/s (Figure 9E,F). However, these higher readings are inconsistent, as there are other areas that are deeply weathered nearby, still fall below 1.0 km/s, which reflects the differential weathering. In addition, the anisotropy analysis of the studied sandstone blocks was conducted and revealed observed variations in internal coherence that were linked to their weatherability. In this term, the block M3-3553 exhibits the highest anisotropy (63.1%) (Figure 9G,H), indicating severe internal heterogeneity due to extensive fractures, laminations, and differential cementation loss. This high degree of anisotropy confirms that the block has suffered from substantial weathering, leading to weakened cohesion and increased vulnerability to mechanical and environmental impact. In addition, the block M1-3577 also shows considerable anisotropy (41%) (Figure 9C,D), which reflects the moderate structural degradation with localized weaknesses that may require targeted consolidation. In contrast, the block M1-3615 (33%) (Figure 9A,B) and the block M2-3502 (22.7%) (Figure 9E,F) display lower anisotropy values, presenting a bit better material resistibility, though still affected by weathering processes.

4. Interventive Conservation Plan

Preventive conservation measures must be implemented against the given role of extreme temperature fluctuations, wind erosion, and groundwater infiltration in the degradation of these blocks. For this, a microclimatic monitoring system should be established to track temperature, humidity, and salt crystallization rates. To reduce thermal stress, shading structures or controlled exposure strategies may be introduced in highly vulnerable areas. Drainage improvements and protective barriers, isolation should be implemented to minimize rising damp and salt damage. In addition, surface encrustations, biological growth, and pollutant residues can accelerate sandstone decay. In this sense, cleaning methods must be non-invasive and material-sensitive to ensure no further damage is inflicted. Dry brushing, deionized water cleaning, and micro-abrasion techniques should be applied to remove superficial dust and salts. For biofilm and lichen removal, pulsed laser cleaning or controlled biocide applications can be considered to ensure environmental safety. Any aggressive chemical cleaning agents must be avoided to prevent long-term stone deterioration and for the high archaeological values of the treated blocks.
Targeted consolidation should be applied to blocks exhibiting visible fractures, laminations, or weakened cohesion. Ethyl silicate-based treatments (often ethyl silicate 40 or similar products) are recommended for this purpose, as they effectively penetrate and polymerization to form a silica gel, strengthening the stone matrix while maintaining the breathability of the stone. It is important to note that ethyl silicate acts primarily as a consolidating agent rather than a protective coating. For surface protection, silane- or siloxane-based water repellents are advised. These materials form a hydrophobic layer that protects the stone from moisture ingress while preserving its physical and chemical structure. Tetraethyl orthosilicate (TEOS), a silica precursor used in sol-gel processes, can also be applied to produce silica-based consolidants or protective coatings [44,45,46]. In cases of extreme fragility, localized structural supports may be necessary to stabilize at-risk blocks before further interventions. Furthermore, to enhance durability while maintaining authenticity, certain sandstone blocks may benefit from nano-silica [47,48,49,50] protective coatings to improve surface cohesion and weather resistance. These coatings must be tested in controlled conditions before large-scale application to ensure compatibility and long-term effectiveness. Any applied treatments should remain reversible and should not alter the original aesthetic and porosity of the sandstone [51].
Finally, scattered blocks should be repositioned within a stable and protective environment to prevent further exposure. This may involve moving some blocks to controlled conservation shelters or creating a designated preservation area within Karnak Temples where the original archaeological context is maintained. For blocks that can be reassembled, digital reconstruction models derived from photogrammetry and 3D scanning will assist in identifying correct placements and structural alignments.

5. Discussion

This study employed a comprehensive multidisciplinary approach, utilizing non-destructive testing (NDT) methods, to assess the physical and mechanical condition and degradation mechanisms of scattered sandstone blocks at the Karnak Temples, a UNESCO World Heritage archaeological site in Egypt. The results highlight the severe deterioration processes affecting these ancient structures, primarily due to prolonged environmental exposure, mechanical damage, and historical interventions. The integrated use of Reflectance Transformation Imaging (RTI), photogrammetry, Infrared Thermography (IRT), Ultrasonic Pulse Velocity (UPV) testing, spectral analysis, gloss analysis, and the Karsten Tube test provided a detailed scientific understanding of the blocks’ condition and the contributing factors to their decay.
A thorough site survey and geolocation mapping were conducted for all blocks within Mastaba 1, 2, and 3 in the northeastern area of Karnak Temples. The archaeological mission successfully assigned new identifiers (UCA codes) to previously unnumbered blocks, ensuring traceability for future conservation and archaeological interpretations. For instance, Mastaba 1 had 21 unnumbered blocks, Mastaba 2 had 3, and Mastaba 3 had 1, all of which were digitally coded.
Detailed observations of four representative blocks (M1-3615, M1-3577, M2-3502, and M3-3553), all dating to the 19th Dynasty under King Seti I, demonstrated varying states of preservation. Block M1-3615, a parallelepiped, showed structural resistance but exhibited weathering, crust formation, biofilm growth, and pictorial layer peeling on its reliefs. Block M1-3577 displayed severe erosion and cracking along horizontal lamination planes, threatening the preservation of its inscriptions. The cylindrical block M2-3502 had relatively well-preserved hieroglyphic reliefs, although later anthropic keying marks were noted. Lastly, Block M3-3553, an inverted fragment with high-relief carvings, presented a deteriorated and sandy upper surface, irregular fractures, salt efflorescence, and biofilm growth.
RTI visualizations effectively presented intricate surface details and degradation patterns not readily apparent through traditional methods. For M1-3615, RTI emphasized tool marks and carved reliefs, aiding in assessing weathering patterns and original carving techniques, despite visible erosion, surface delamination, and minor cracking. On M1-3577, RTI highlighted surface pitting, abrasions, and remnants of Egyptian blue pigment, with close-ups exposing microfractures and small-scale flaking. M2-3502 showed areas of crisp and deteriorated inscriptions, particularly at the base, where granular disintegration was evident. Finally, RTI on M3-3553 demonstrated erosion in lower sections, with enhanced views improving the readability of shallow carvings and revealing micro-topographic features. In this context and in alignment with the current study application, Barack et al. [52] applied Reflectance Transformation Imaging (RTI) primarily to the study of ancient glass objects. While their focus was on a different material, their methodology offers valuable parallels for broader archaeological applications. Their work not only highlights RTI’s effectiveness in detecting and documenting surface-level changes associated with ongoing material decay but also provides significant technical understanding into optimizing lighting, angle calibration, and image processing for enhanced surface analysis. In addition, Saha et al. [53] confirmed the importance of applying RTI for surface monitoring and tracking deterioration over time. Their study demonstrated that RTI can not only visualize archaeological surface features in high detail but also support condition assessment by qualitatively and semi-quantitatively evaluating changes.
Photogrammetry facilitated precise digital reconstruction and documentation, allowing for comprehensive analysis of the blocks’ physical condition and archaeological significance. The 3D models captured fine details such as inscriptions, tool marks, and weathering patterns. M1-3615, likely a column or wall fragment, showed severe weathering, striations, and black deposits due to prolonged humidity. M1-3577, part of an inscribed wall or frieze, displayed high surface erosion affecting inscription clarity, fragile edges, and discoloration indicating ongoing chemical weathering. M2-3502, a column section, had relatively well-preserved inscriptions but exhibited cracks and material loss at the lower parts, indicating structural weaknesses. M3-3553, a wall fragment, showed chipped edges, wear, and surface encrustations that indicate a high risk of mechanical damage and salt crystallization. In line with Haddad [54], the detailed 3D models created through photogrammetry thus serve not only as precise documentation tools but also as a means of promoting heritage knowledge and enabling informed conservation decisions without risking misleading or inauthentic representations.
Spectral and gloss analysis demonstrated variations in the surface condition of the sandstone blocks. For M1-3615, lightness (L*) values indicated areas of darker discoloration from soiling and moisture, alongside lighter sections indicating surface erosion. Low gloss values (0.5–2.5%) consistently reflected a rough, weathered surface. M1-3577 exhibited wider L* variations, with darker areas linked to heavy soiling and biological growth, and a notably high chroma (81.34) in one measurement, indicating distinct pigment concentration or mineral deposits. M2-3502 showed darkening due to surface soiling and moderate red and yellow hues that could refer to iron oxide staining, with very low gloss (0.8–1.8 GU) indicative of granular disintegration and micro-cracking. Accordingly, these results align well with the study of Benavente et al. [55], who demonstrated that color changes in building stones are predominantly influenced by surface roughness rather than chemical alterations of the stone’s chromophores. Their study showed that weathering processes, such as acid attack or physical erosion, induce measurable shifts in lightness and chroma primarily due to changes in surface texture. This reinforces the interpretation that the observed discoloration and gloss variations in our blocks reflect physical surface degradation processes such as erosion, biological colonization, and micro-cracking, rather than purely chemical changes.
Infrared thermography demonstrated observed diurnal temperature fluctuations on the sandstone surfaces, peaking around 60.6 °C in the afternoon and dropping to 22.1 °C in the early morning. This substantial thermal stress causes micro-expansion and contraction, leading to microcracks, granular disintegration, and surface exfoliation. The sandstone’s porosity increases this effect, as moisture within pores rapidly evaporates under high temperatures, creating pressure that weakens the stone. The presence of salts further intensifies damage through crystallization. This thermal decay directly correlates with observed sandstone degradation patterns such as scaling, powdering, sanding, and crust formation, with decay being most pronounced on sun-exposed surfaces. These observations are in agreement with Zhang et al. [56], who used IRT in combination with 3D laser scanning to examine thermal-induced blistering and decay on the Vajrasana pagoda. Their integrated approach showed that thermal stress concentrations were a major driver of subsurface delamination and surface deformation. Through the fusion of thermal and geometric datasets, their study successfully pinpointed early-stage damage areas and forecasted zones of fracture risk via finite element modeling. Similarly, in the current study, thermal readings, when combined with visual inspection and photogrammetric documentation, support the interpretation that recurring thermal stress plays a decisive role in the mechanical breakdown of the sandstone.
Karsten Tube tests provided a deep look into the water absorption properties and capillary water transport of the sandstone blocks, reflecting variations in stone density, pore structure, and prior weathering. Block M1-3615 and M2-3502 displayed high-water absorption coefficients (0.031 kg/m2s) and rates (0.5 mL/s), indicating open pore networks susceptible to accelerated decay from salt crystallization and thermal cycling. In contrast, M1-3577 showed lower absorption (0.018 kg/m2s, 0.1 mL/s), indicating reduced porosity, which, while slowing water-induced decay, could lead to sub-surface salt entrapment. M3-3553 exhibited the lowest values (0.006 kg/m2s, 0.03 mL/s), implying minimal water penetration but also potentially prolonged internal moisture exposure due to reduced drying capacity. In this sense, the analytical interpretation presented by Hendrickx [20], who emphasized that while the Karsten tube supplies practical, non-destructive measurements of water absorption, a more comprehensive understanding arises when these readings are paired with models that account for capillary saturation and sorptivity. His study, through 3D numerical simulations and moisture front tracking, demonstrated how material microstructure governs water transport and retention. Applying these to our site, the higher sorptivity and capillary moisture saturation inferred from the Karsten test results on blocks like M1-3615 reinforce their susceptibility to accelerated decay, particularly under thermal and saline stresses identified through complementary methods such as infrared thermography.
The ultrasonic pulse velocity (UPV) results clearly reflect the internal condition and weathering extent of the studied sandstone blocks, demonstrating important variations in structural resilience. Lower UPV values (0.2–0.8 km/s) were associated with severely deteriorated areas marked by fractures, laminations, and internal voids, while moderately weathered zones displayed intermediate values (1.5–2.0 km/s) that indicate partial coherence of the stone fabric. Healthier sections approached 2.0 km/s but still remained below typical values for pristine sandstone, reflecting overall degradation. Anisotropy analysis further emphasized this heterogeneity, with block M3-3553 showing the highest anisotropy (63.1%) and M1-3577 (41%), both indicating severe internal damage and weatherability. In contrast, blocks M2-3502 (22.7%) and M1-3615 (33%) exhibited relatively better internal cohesion. In this regard and closely to the current study, Centauro et al. [57] mentioned that a state of medium to high degradation in the Pietraforte sandstone facades of the Palazzo Medici Riccardi is indicated by Vp values lower than 2.0 km/s due to open fractures, detachments, or superficial disintegration. In addition, in their study, the ultrasonic pulse velocity (Vp) values for the investigated blocks were found to be between 4 and 5 km/s for healthier sandstone in the facades.

6. Conclusions

The present study highlights the effectiveness of non-destructive testing methods in assessing the physical and mechanical condition and conservation needs of scattered sandstone blocks at Karnak Temples, Luxor.
The RTI and photogrammetry analyses provided a valuable look into the surface morphology of the blocks, showing erosion patterns, tool marks, and inscriptions, enhancing visibility of the inscriptions and fine surface textures that aid in future epigraphic studies and historical reconstructions. In addition, photogrammetry generated precise 3D models that can be used for future conservation and reconstruction intervention efforts. Moreover, Infrared thermography demonstrated high temperature variations across the blocks, with peak thermal stress reaching 60.6 °C in the afternoon, which led to expansion-contraction cycles that exacerbate microcracking and surface delimitation. While the maximum temperature does not directly cause stone alteration, it is the rapid thermal fluctuations, commonly referred to as thermal jumps, and particularly the speed at which these changes occur, that generate stress conditions within the stone matrix [58]. The presence of moisture-related anomalies was also detected, indicating potential areas susceptible to further degradation due to salt crystallization and humidity fluctuations, confirmed by the high capillary water uptake, increasing their susceptibility to mechanical and chemical weathering. For this, the study found high differences in velocity values across the examined blocks, with deteriorated zones, indicative of fractures, decohesion of the grains, and/or variation of the porosity. Moreover, the spectral and gloss analysis highlighted variations due to weathering, with low gloss values indicating high surface roughness and material loss. Finally, effective interventive conservation for the sandstone blocks requires continuous monitoring of microclimate conditions and the implementation of shading, drainage, and protective barriers. In this sense, the results demonstrate that environmental factors, particularly thermal fluctuations, wind erosion, and ambient humidity, severely affected the structural durability of these ancient blocks, leading to microcracking, granular disintegration, and surface delamination. Additionally, scattered blocks should be reassembled using the scanned digital models to ensure the preservation of their original archaeological context [59].

Author Contributions

Conceptualization, A.F., S.D.-B. and E.M.-P.; methodology, A.F., S.D.-B., A.D.-M., F.M.-V. and E.M.-P.; formal analysis, A.F., S.D.-B., A.D.-M., F.M.-V. and E.M.-P.; investigation, A.F., S.D.-B., A.D.-M., F.M.-V. and E.M.-P.; resources, S.D.-B. and E.M.-P.; data curation, A.F., S.D.-B. and E.M.-P.; writing original draft preparation, A.F.; writing, review and editing, S.D.-B., A.D.-M., F.M.-V. and E.M.-P.; supervision, S.D.-B. and E.M.-P.; project administration, A.F. and E.M.-P.; funding acquisition, S.D.-B. and E.M.-P. All authors have read and agreed to the published version of the manuscript.

Funding

The first campaign of the Spanish-Egyptian Archaeological Mission has been funded through research grants and a “special action” from the University of Cádiz’s Own Plan through the Vice-Rector’s Office for Research and Knowledge Transfer, as well as the Instituto Universitario de Investigación Marina (INMAR) and the CEI-Mar Foundation.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author(s).

Acknowledgments

We acknowledge the University of Cádiz for supporting the Spanish-Egyptian Archaeological Mission (Karnak Stones Project; https://karnakstonesproject.com/) at Karnak Temples, Luxor (Concession 2024). Additionally, we express our gratitude to the Department of Earth Sciences (UGEA-PHAM service, University of Cádiz) for providing the necessary infrastructure and equipment for archaeological fieldwork and testing part. We also extend our appreciation to Stefan Simon, director of Rathgen Research Laboratory, National Museums of Berlin, for supplying the portable spectrophotometer and glossmeter essential for our analysis.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
NDTNon-destructive testing
RTIReflectance Transformation Imaging
IRTInfrared Thermography
UPVUltrasonic Pulse Velocity
KSPKarnak Stones Project (https://karnakstonesproject.com/)
H-RTIHighlight Reflectance Transformation Imaging
PTMPolynomial texture mapping
SCESpecular component excluded
WCWater absorption coefficient (kg/m2√s)
VVolume
AArea
tTime
WWater absorption coefficient (mL/s)
TTransmitter
RReceiver
M1-M2-M3Mastaba ID
UCAUniversity of Cádiz

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Figure 1. General plan for Karnak complex (in yellow and brown) and the Sacred Lake (in blue), including the Mastabas (in red) carrying thousands of stone blocks from 1 to 6 (zones), these zones are a plan for the mission for comprehensive preservation plan for Karnak Stones Project (KSP) (A). In 2024 concession, condition assessment carried out in zone 1, in the northeast corner of Karnak Temples, and some selected stone blocks are under study in the current research (B).
Figure 1. General plan for Karnak complex (in yellow and brown) and the Sacred Lake (in blue), including the Mastabas (in red) carrying thousands of stone blocks from 1 to 6 (zones), these zones are a plan for the mission for comprehensive preservation plan for Karnak Stones Project (KSP) (A). In 2024 concession, condition assessment carried out in zone 1, in the northeast corner of Karnak Temples, and some selected stone blocks are under study in the current research (B).
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Figure 2. Site planimetry and geolocation of the blocks in the northeastern area at Karnak Temples. The four selected case blocks for the study labelled as M1-3615, M1-3577, M2-3502, and M3-3553. UCA label refers to the University of Cádiz.
Figure 2. Site planimetry and geolocation of the blocks in the northeastern area at Karnak Temples. The four selected case blocks for the study labelled as M1-3615, M1-3577, M2-3502, and M3-3553. UCA label refers to the University of Cádiz.
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Figure 3. Reflectance Transformation Imaging (RTI) shows detailed surface conditions of inscribed sandstone blocks M1-3615, M1-3577, M2-3502, and M3-3553. Specular and PTM renderings enhance visibility of tool marks (M2-3502), pigment traces (M1-3615), and weathering features (M1-3577, M1-3615, and M3-3553). Close-ups highlight microfractures, erosion, and evidence of ancient carving techniques (M1-3615 and M2-3502). These visualizations support conservation analysis and epigraphic interpretation. The red bar represents 50 cm.
Figure 3. Reflectance Transformation Imaging (RTI) shows detailed surface conditions of inscribed sandstone blocks M1-3615, M1-3577, M2-3502, and M3-3553. Specular and PTM renderings enhance visibility of tool marks (M2-3502), pigment traces (M1-3615), and weathering features (M1-3577, M1-3615, and M3-3553). Close-ups highlight microfractures, erosion, and evidence of ancient carving techniques (M1-3615 and M2-3502). These visualizations support conservation analysis and epigraphic interpretation. The red bar represents 50 cm.
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Figure 4. Photogrammetric 3D models of four architectural blocks from Karnak, shown from multiple perspectives. Block 1 shows severe weathering and black deposits; Block 2 features hieroglyphs and pigment remains with surface erosion; Block 3 is a column drum with cracks and material loss; Block 4 is a wall fragment with chipped and eroded edges and salt encrustations. The red bar represents 50 cm.
Figure 4. Photogrammetric 3D models of four architectural blocks from Karnak, shown from multiple perspectives. Block 1 shows severe weathering and black deposits; Block 2 features hieroglyphs and pigment remains with surface erosion; Block 3 is a column drum with cracks and material loss; Block 4 is a wall fragment with chipped and eroded edges and salt encrustations. The red bar represents 50 cm.
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Figure 5. Spatial distribution of the measurement points (blue dots) for spectral and gloss analyses on each studied block and showed in Table 2.
Figure 5. Spatial distribution of the measurement points (blue dots) for spectral and gloss analyses on each studied block and showed in Table 2.
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Figure 6. Infrared thermography analysis plotting of the four representative blocks. The blue, orange, and red colors represent the temperature records at 6:30, 8:30, and 15:30, respectively, for each block.
Figure 6. Infrared thermography analysis plotting of the four representative blocks. The blue, orange, and red colors represent the temperature records at 6:30, 8:30, and 15:30, respectively, for each block.
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Figure 7. IR thermography surface analysis of the studied sandstone blocks in various durations per day.
Figure 7. IR thermography surface analysis of the studied sandstone blocks in various durations per day.
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Figure 8. Water absorption coefficient parameters WC of Karsten tube penetration test (left) and water absorption rates W (speed) (right).
Figure 8. Water absorption coefficient parameters WC of Karsten tube penetration test (left) and water absorption rates W (speed) (right).
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Figure 9. Isometric representation of UPV results of the studied blocks M1-3615 (A), M1-3577 (C), M2-3502 (E), and M3-3553 (G), and ultrasonic analysis M1-3615 (B), M1-3577 (D), M2-3502 (F), M3-3553 (H). Highest pulse velocity (in yellow) and lowest velocity (in purple). Yellow line in (E,G) refers to fracture.
Figure 9. Isometric representation of UPV results of the studied blocks M1-3615 (A), M1-3577 (C), M2-3502 (E), and M3-3553 (G), and ultrasonic analysis M1-3615 (B), M1-3577 (D), M2-3502 (F), M3-3553 (H). Highest pulse velocity (in yellow) and lowest velocity (in purple). Yellow line in (E,G) refers to fracture.
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Table 1. Detailed site observation of the representative blocks.
Table 1. Detailed site observation of the representative blocks.
Block IDLocation (East Wall, Sector B)Dimensions (Width, Length, and Height, in cm)Dynasty and KingDescription and FeaturesCondition and Observations
3615Mastaba 1 100 × 120 × 60 19th Dynasty, Seti IParallelepiped sandstone block with front face reliefs (city of Behdet, wings, wheel). Hole in the upper face for joining blocks. Mortar-filled cavities with Egyptian blue pigment; traces of white paint.Structurally intact but weathered. Crust partially covers reliefs. Biofilms and pictorial layer peeling. Cross lamination present.
3577Mastaba 1 160 × 75 × 40 19th Dynasty, Seti ISandstone block with inscriptions on the west face. Upper face has a 12 mm-wide keying mark. Irregular faces, altered microstructure.Significant erosion and cracking along horizontal lamination planes. Conservation measures needed to protect inscriptions.
3502Mastaba 2 90 (height) × 220 (diameter) 19th Dynasty, Seti ICylindrical sandstone block with lower zone hieroglyphic reliefs and cartouches. Upper part finely chiseled with dovetail joints. Rear surface retains white mortar traces.Well-preserved walls. No polychrome remains. Later anthropic keying marks, some repaired with mortar.
3553Mastaba 3145 × 85 × 6519th Dynasty, Seti ISandstone block with high-relief carvings (sun symbol, vulture, Seti I cartouches). Inverted orientation. Inscription mentioning “Sḫt ȝt Mr.t Ptḥ”Upper surface deteriorated and sandy. Irregular fractures, salt efflorescence, biofilm growth. Despite weathering, carvings remain important for further study.
Table 2. Colorimetry (L*, a*, b*, Hue, Chroma, and pseudo color) and gloss (GU) analysis for sandstone blocks.
Table 2. Colorimetry (L*, a*, b*, Hue, Chroma, and pseudo color) and gloss (GU) analysis for sandstone blocks.
L*a*b*HueChromaGU (%)Pseudo Color
M1-33615161.516.2617.617018.690.5Heritage 08 00320 i001
257.696.7017.776918.991.3Heritage 08 00320 i002
368.232.0211.588011.750.8Heritage 08 00320 i003
469.954.9116.047215.912.5Heritage 08 00320 i004
M1-3577157.765.5316.617217.502.7Heritage 08 00320 i005
260.845.9717.697118.672.3Heritage 08 00320 i006
354.905.5516.457117.364.2Heritage 08 00320 i007
443.036.6520.297221.321.5Heritage 08 00320 i008
M2-3502162.126.0117.687118.670.8Heritage 08 00320 i009
263.155.1915.5171.516.361.7Heritage 08 00320 i010
358.256.2416.246917.401.8Heritage 08 00320 i011
454.286.9217.5970.518.661.4Heritage 08 00320 i012
M3-3553161.775.8316.957117.922.3Heritage 08 00320 i013
260.946.9119.527120.700.5Heritage 08 00320 i014
350.496.1816.997018.073.8Heritage 08 00320 i015
477.992.1115.988216.114.3Heritage 08 00320 i016
Table 3. Ultrasonic Pulse Velocity (UPV) measurements for studied sandstone blocks with measurement path, type, and velocity.
Table 3. Ultrasonic Pulse Velocity (UPV) measurements for studied sandstone blocks with measurement path, type, and velocity.
Block IDPath LabelMeasurement TypeDistance (cm)Velocity (km/s)
M1-36151–12Semidirect150.2
2–11Semidirect150.4
3–10Semidirect150.6
4–9Semidirect150.9
5–8Semidirect151.1
6–7Semidirect151.3
7–8Direct (L1)101.4
8–9Direct (L1)101.45
9–10Direct (L1)101.55
10–11Direct (L1)101.6
13–14Direct (L2)101.6
14–15Direct (L2)101.5
15–16Direct (L2)101.4
16–17Direct (L2)101.3
17–18Direct (L2)101.2
18–19Direct (L2)101.1
20–21Direct (L3)100.9
21–22Direct (L3)100.8
22–23Direct (L3)100.6
23–24Direct (L3)100.45
24–25Direct (L3)100.3
25–26Direct (L3)100.2
M1-35771–2Direct (L1)101.2
2–3Direct (L1)101.3
3–4Direct (L1)101.35
4–5Direct (L1)101.45
6–7Direct (L2)101.3
7–8Direct (L2)101.35
8–9Direct (L2)101.45
9–10Direct (L2)101.5
11–12Direct (L3)101.3
12–13Direct (L3)101.2
13–14Direct (L3)101.1
14–15Direct (L3)101
M2-35021–1Semidirect
(NE Corner)		152
2–2Semidirect
(NE Corner)		151.85
3–3Semidirect
(NE Corner)		151.7
4–4Semidirect
(NE Corner)		151.5
5–6Direct 101.25
6–7Direct 101
7–8Direct 100.75
8–9Direct 100.6
9–10Direct 100.45
10–11Direct 100.3
11–12Direct 100.2
12–13Direct 100.15
13–14Direct 100.1
M3-35531–1Semidirect
(NE Corner)		151.8
2–2Semidirect
(NE Corner)		151.65
3–3Semidirect
(NE Corner)		151.4
4–4Semidirect
(NE Corner)		151.1
1–5Direct (L1)101.2
2–6Direct (L1)101
3–7Direct (L1)100.8
4–8Direct (L1)100.6
5–9Direct (L1)100.45
2–10Direct (L2)100.9
3–11Direct (L2)100.75
4–12Direct (L2)100.6
5–13Direct (L2)100.45
6–14Direct (L2)100.3
1–2Direct (Crack)100.2
2–3Direct (Crack)100.15
3–4Direct (Crack)100.1
4–5Direct (Crack)100.08
5–6Direct (Crack)100.05
6–7Direct (Crack)100.03
7–8Direct (Crack)100.02
8–9Direct (Crack)100.01
9–14Direct (Crack)100
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Fahmy, A.; Domínguez-Bella, S.; Durante-Macías, A.; Martínez-Viñas, F.; Molina-Piernas, E. Integrated Documentation and Non-Destructive Surface Characterization of Ancient Egyptian Sandstone Blocks at Karnak Temples (Luxor, Egypt). Heritage 2025, 8, 320. https://doi.org/10.3390/heritage8080320

AMA Style

Fahmy A, Domínguez-Bella S, Durante-Macías A, Martínez-Viñas F, Molina-Piernas E. Integrated Documentation and Non-Destructive Surface Characterization of Ancient Egyptian Sandstone Blocks at Karnak Temples (Luxor, Egypt). Heritage. 2025; 8(8):320. https://doi.org/10.3390/heritage8080320

Chicago/Turabian Style

Fahmy, Abdelrhman, Salvador Domínguez-Bella, Ana Durante-Macías, Fabiola Martínez-Viñas, and Eduardo Molina-Piernas. 2025. "Integrated Documentation and Non-Destructive Surface Characterization of Ancient Egyptian Sandstone Blocks at Karnak Temples (Luxor, Egypt)" Heritage 8, no. 8: 320. https://doi.org/10.3390/heritage8080320

APA Style

Fahmy, A., Domínguez-Bella, S., Durante-Macías, A., Martínez-Viñas, F., & Molina-Piernas, E. (2025). Integrated Documentation and Non-Destructive Surface Characterization of Ancient Egyptian Sandstone Blocks at Karnak Temples (Luxor, Egypt). Heritage, 8(8), 320. https://doi.org/10.3390/heritage8080320

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