Application and Challenges of Chinese Lacquer Identification Techniques in the Conservation of Cultural Relics

Abstract

Chinese lacquer, a natural polymer with exceptional durability and cultural significance, has been widely used since the Warring States period. This review examines recent advances in lacquer identification techniques and their role in cultural heritage conservation. Drawing on five representative case studies—the B54 Japanese armor, Ba lacquerware from Lijiaba, a Qing Dynasty folding fan, Ryukyu lacquerware, and late Joseon objects—we show how integrated analytical approaches combining microscopy, spectroscopy, chromatography, and biochemical methods provide critical insights into composition, degradation, and conservation strategies. Key findings highlight (1) the effectiveness of multi-technique analysis in characterizing complex lacquer–metal interfaces and layered structures; (2) the recognition of regional and chronological variations in lacquer formulations, highlighting the need for standardized authentication protocols and shared databases; and (3) the promise of non-destructive technologies to reduce sampling and improve aging simulations. By critically synthesizing these case studies, the review highlights both methodological successes and persistent challenges, such as ethical constraints of sampling and limited understanding of long-term degradation. Ultimately, lacquer is positioned at the intersection of material science and cultural preservation, offering a transferable framework for global heritage protection. Future directions include hyperspectral imaging, bioinspired consolidants, and computational modeling to advance non-invasive diagnostics and sustainable conservation.

1. Introduction

Chinese lacquer, a unique natural polymer material, has been in widespread use since the Warring States period in China. It has been applied in various fields such as decoration, furniture, architecture, arts and crafts, and even serves as an anti-corrosion coating for undersea optical cables. Additionally, it has traditional medicinal applications [1]. The natural lacquer’s remarkable film-forming properties, durability, and aesthetic value have granted it profound cultural significance and historical importance, especially in Chinese lacquer art.

Lacquerware unearthed from regions across northern and southern China, as well as in Japan and Korea, exhibits outstanding qualities—vivid appearances, strong corrosion resistance, and excellent waterproof performance [2]. Particularly during the Warring States and Han dynasties, black and vermilion lacquer decorations, often combined with gold and silver inlays, were commonly applied to everyday vessels, weapons, and ceremonial implements, thereby defining a distinctive craft style characteristic of that period [3]. In later times, as porcelain became the preferred material for everyday vessels, lacquerware gradually lost its role in tableware. Nevertheless, due to its refined qualities and durability, lacquer art continued to play a significant role in the cultural life of scholars and literati, particularly in the production of temple furnishings, decorative objects, and desk items (

Table 1. Application of Chinese lacquer in the finishing of various materials.

Types of Items	Applications [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]
Wooden substrate	Polychrome clay figurines in Guanyin Temples, lacquered wooden nails with cloud patterns, cooking utensils, figurines, ceremonial trays, lacquered saddles, trays, decorative lacquerware
Bamboo substrate	Lacquered Qiong bamboo furniture, temple implements, and traditional objects in Taiwan
Metal substrate	Ancient steel weapons, coffins, trays, cups
Leather substrate	Lacquered document folders, archaeologically excavated saddles, lacquered cosmetic boxes, ancient leather headgear, and belts
Ceramic or clay substrate	Lacquer clay sculptures commonly found in Buddhist statues and altar decorations
Composite and modern materials	Creative experiments in lacquer art within educational contexts
Others	Sculpture ornamentation

).

This review was conducted by systematically searching peer-reviewed articles and case studies published from 2000 to 2025 in databases including Web of Science, Scopus, Google Scholar, and CNKI. Keywords such as “Chinese lacquer”, “urushiol analysis”, “Py-GC/MS lacquer”, “lacquer degradation”, and “spectroscopy lacquer heritage” were used in combination. Both Chinese and Western research were considered to ensure a balanced international perspective. Priority was given to studies that reported detailed methodology, provided analytical spectra, or were applied to real cultural heritage conservation cases.

While earlier reviews have explored the chemistry of urushiol and analytical methods in isolation, they often lack integration between technique and practice. For example, Webb (2000) [19] and Kumanotani (1995) [20] provided foundational insights into lacquer’s chemical behavior and durability, but offered limited guidance on how modern analytical tools can aid in conservation strategy. More recent Chinese literature has emphasized stratigraphic microscopy and case-based conservation outcomes, but still lacks a comprehensive framework for method selection. Additionally, many Western studies overlook region-specific formulations such as laccol or thitsi (the traditional term for the natural, thitsiol-based phenolic lacquer resin sourced from the Gluta usitata tree, predominantly used in Myanmar to create lacquerware).

Unlike previous works, this review emphasizes a multi-technique integration approach and its direct application to conservation decision-making. Rather than focusing solely on the capabilities of analytical tools, we aim to bridge the gap between material science and conservation practice. By organizing the discussion around real-world case studies and technical challenges (e.g., delamination, pigment instability, substrate interactions), the review seeks to serve both scientists and restorers.

The identification and authentication of natural lacquer are crucial in the conservation and restoration of cultural relics. However, lacquer’s natural bio-based properties make it susceptible to degradation caused by environmental factors such as hydrolysis, ultraviolet radiation, and microbial activity during preservation [16]. This presents significant challenges in the conservation and authentication of lacquer artifacts.

In recent years, advancements in analytical chemistry and materials science have contributed to a deeper understanding of lacquer composition, aging mechanisms, and synthetic alternatives, providing scientific support for the restoration and authenticity verification of lacquer artifacts [7]. Techniques like Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and gas chromatography–mass spectrometry (GC-MS) have been widely employed to analyze the structure of lacquer materials and their degradation byproducts. Additionally, emerging methods that combine microscopy with AI-powered image recognition have shown great potential for stratigraphic imaging and micro-trace detection of lacquer layers [17].

Despite these advances, a comprehensive consolidation of existing techniques and their practical utility in conservation strategies remains insufficient. Furthermore, the lack of standardized workflows and cross-study comparability hinders the development of globally applicable best practices.

This paper systematically reviews the recent research on Chinese lacquer materials and their authentication technologies from six key perspectives (Figure 1): (1) application studies in both traditional and contemporary fields; (2) chemical composition and molecular structural characteristics; (3) mechanisms of lacquer film aging and deterioration; (4) new advancements in analytical authentication techniques; (5) innovative applications in cultural heritage conservation; and (6) research prospects and conclusions. The goal is to provide a state-of-the-art reference that combines technical precision with practical relevance for researchers, restorers, and cultural heritage professionals.

2. Chemical Composition and Deterioration Characteristics of Chinese Lacquer

The chemical composition and deterioration characteristics of Chinese lacquer, along with the factors that accelerate its degradation, form the foundation for the identification of lacquer components in cultural relics.

2.1. Chemical Composition

Chinese lacquer is a natural coating material primarily sourced from the sap of trees in the Anacardiaceae family, with the lacquer tree (Toxicodendron vernicifluum, formerly known as Rhus vernicifera) being the most common source. The sap is extracted by making incisions in the tree bark and appears as a grayish-white or pale-yellow milky substance. As it dries, it gradually darkens to a brown color and possesses strong adhesion and gloss [21]. The active compound in Chinese lacquer is urushiol, a type of catechol derivative with unsaturated hydrocarbon side chains that are either C15 or C17 in length [22].

Table 2. Comparison of core components, curing process, and properties of the three major traditional lacquers.

Component	Chinese Lacquer (Urushi)	Japanese Lacquer (Urushiol)	Vietnamese Lacquer (Laccol)
Main Compound	Urushiol (C15/C17 unsaturated side chains)	Urushiol (C15/C17 unsaturated side chains)	Laccol (more saturated structure)
Film-Forming Agent	Urushiol	Urushiol	Laccol
Curing Process	Enzyme-catalyzed oxidative polymerization	Enzyme-catalyzed oxidative polymerization	Similar, but slower curing due to more saturated structure
Properties	Strong adhesion, high gloss, resistant to moisture, corrosion, and UV	Similar properties to Chinese lacquer, but slightly harder and more durable	Less glossy, slower drying, more flexible

outlines its components. These components work together to form a hard lacquer film with waterproof, anti-corrosive, and antibacterial properties through enzyme-catalyzed oxidative polymerization in the air [23].

Lacquer sap from different geographical regions (e.g., China’s urushi, Japan’s urushiol, and Vietnam’s laccol) differs slightly in the saturation of their side chains and film-forming properties. Both Japanese and Chinese lacquers primarily contain C15/C17 unsaturated alcohols, whereas Vietnamese laccol tends to have a more saturated structure [24]. These subtle differences in composition affect the color, drying speed, and flexibility of the lacquer coating. Table 2 summarizes the key differences in chemical composition and curing behavior among Chinese, Japanese, and Vietnamese lacquers. These differences impact not only the final appearance and hardness of the lacquer but also its deterioration characteristics over time.

In addition, due to the inherent properties of lacquer, in practical applications, artisans often supplement the lacquer with various plant oils—such as bodying linseed oil, perilla oil, and tung oil [24]—to reduce the viscosity of the liquid lacquer, thereby facilitating brush application and improving its leveling properties. Additionally, proteins such as pig’s blood, animal glue [25], and egg may be incorporated into the ground layers of Asian lacquer as binders. Furthermore, the addition of pig bile can thin the lacquer, thereby minimizing visible brush marks to the greatest extent possible [26].

2.2. Deterioration Characteristics

Lacquer plays a crucial role in cultural heritage as both a decorative and protective layer. Its deep color gloss, transparency, and color saturation make it ideal for techniques like gold powder painting, mother-of-pearl inlay, and other artistic processes, creating a lacquer film with a jade-like sheen [27]. Beyond aesthetic value, lacquer often carries symbolic patterns and is commonly seen in lacquered stationery, luxury boxes, and religious artifacts. Its resistance to moisture, corrosion, and insects makes it an effective protective layer on materials such as wood, bamboo, leather, and metal [28], significantly slowing down degradation and biological invasion in humid environments.

However, over time, factors such as light exposure and temperature fluctuations, and humidity variations lead to the degradation of lacquer. Unlike modern coatings, once lacquer films oxidize, they are difficult to restore to their original state. The inclusion of mineral components like cinnabar and iron powder in early lacquerware accelerates lacquer degradation, creating challenges in restoration [29].

Light aging is one of the main causes of lacquer degradation, as lacquer phenols and enzyme-catalyzed polymers undergo oxidation, generating free radicals and quinone structures (such as para-benzoquinone, ortho-benzoquinone), which are highly polar and are the primary cause of color change [30]. Over prolonged light exposure, the benzene ring structure of the lacquer is broken down, leading to small molecular oxidation products (such as carboxylic acids, aldehydes, etc.), weakening the lacquer film’s original rigidity and making it brittle. Furthermore, the alternating heat and humidity environment accelerates lacquer degradation due to inconsistent expansion rates in composite lacquer layers, leading to bubbling, warping, or cracking [31].

In addition, acidic and alkaline environments, along with mechanical damage, contribute to lacquer degradation. Exposure to acid or alkaline environments degrades the proteins and enzymes in the lacquer, causing local instability [32]. The lacquer film can suffer from cracking, curling, or other types of damage due to corrosion or external force. In summary, the degradation of lacquer not only affects its decorative effect but also compromises its protective function, making it more challenging to authenticate and restore cultural artifacts [33].

It is noteworthy that, according to some relevant studies, under certain conditions, the additives present in lacquer—such as oils—can exert a more significant influence on its aging characteristics than the specific type of lacquer itself [34].

3. Identification Techniques for Chinese Lacquer

The identification and characterization of Chinese lacquer rely on a range of complementary analytical methods designed to reveal its complex chemical composition, degradation behavior, and multi-layered structural morphology. These methods include spectroscopic, chromatographic, microscopic, and biochemical techniques. Each contributes distinct types of information—functional group detection, molecular profiling, structural stratigraphy, or species-level source identification—and their combined use has become standard practice in cultural heritage research and restoration.

3.1. Spectroscopic Techniques

Spectroscopic techniques provide molecular-level insights into the lacquer film through the interaction of light with its chemical components. They are widely used to identify organic functional groups, track oxidative degradation, and monitor polymerization or crosslinking reactions [35]. Among these, Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy are the most frequently employed.

3.1.1. Fourier-Transform Infrared Spectroscopy (FTIR)

Fourier-transform infrared spectroscopy (FTIR) is one of the most widely used and technically mature analytical tools in the characterization of lacquer materials. It plays a foundational role in cultural heritage conservation by enabling the identification of key functional groups and monitoring chemical transformations in lacquer films over time [36,37,38]. Through the interaction of infrared radiation with molecular vibrations, FTIR reveals characteristic absorption bands corresponding to hydroxyl (–OH), carbonyl (C=O), alkane chains, aromatic rings, and other molecular moieties commonly found in urushiol-based lacquers.

To adapt to the varying conservation contexts and sampling limitations inherent in heritage analysis, FTIR has evolved into several instrumental configurations, each with distinct methodological advantages:

• Traditional transmission-mode FTIR requires finely ground micro-samples, typically prepared as KBr pellets. While destructive—as it necessitates grinding samples into KBr pellets, rendering it unsuitable for precious cultural artifacts [37]—it offers high spectral resolution and is used extensively in laboratory settings for establishing reference spectra and conducting compositional benchmarking. While some contemporary studies still utilize conventional FTIR, its application is predominantly restricted to laboratory-simulated specimens or archaeological lacquerware, enabling micro-sampling. For instance, an investigation of Han Dynasty lacquerware from a tomb in Mianyang, Sichuan, employed FTIR in conjunction with SEM-EDS, though analysis was confined to minute fragments that could be ethically acquired [38].
• ATR-FTIR (attenuated total reflectance) is the most commonly used mode in conservation practice due to its surface-level sensitivity and ability to acquire data with minimal sampling, sometimes from flakes or micro-stratified cross-sections. It is especially effective for investigating layered structures, revealing differences between undercoats, ground layers, and top films in composite lacquer systems. However, it is noteworthy that ATR probes may leave indentations on fragile lacquer films, while highly reflective surfaces are prone to scattering artifacts. This technique is also limited in analyzing thick lacquer coatings or deep aging patterns. In the study of ancient lacquer films, ATR-FTIR combined with chemometrics has enabled quantitative analysis of lacquer and drying oils [37].
• ER-FTIR (external-reflectance FTIR) enables non-contact, in situ analysis directly on object surfaces, making it invaluable in museum environments where sampling is restricted or prohibited. While its signal-to-noise ratio is lower—especially for organic phases—it provides preliminary molecular fingerprinting to support broader conservation assessments. ER-FTIR remains in the exploratory phase for lacquerware research, yet exhibits unique value for non-sampling cultural relics. Currently, analogous techniques have been applied to studies of photographic materials [39], mural pigments [40], and historical textiles and leather [41], among other cultural heritage materials. However, the application of ER-FTIR in lacquerware research remains relatively limited. Furthermore, this method exhibits certain technical limitations. For instance, highly polished lacquer surfaces (e.g., burnished lacquer) are prone to specular reflection, which may cause spectral distortion and consequently affect the reliability of analytical results.

FTIR has been particularly successful in diagnosing lacquer degradation. The emergence or intensification of carbonyl absorption bands near 1710 cm⁻¹ is a widely recognized spectral marker of urushiol oxidation, indicating photochemical aging and discoloration [38,39,40,41,42,43,44]. Additionally, FTIR can detect quinone formation, which is associated with the darkening and brittleness of aged lacquer films. Quinone formation is spectroscopically confirmed by the appearance of a strong carbonyl (C=O) stretching band typically in the 1690–1640 cm⁻¹ region of the FTIR spectrum. This diagnostic peak is often accompanied by the simultaneous attenuation or loss of the broad hydroxyl (O-H) band associated with the precursor phenol, typically found around 3600–3200 cm⁻¹. These spectral changes not only inform conservators about the artifact’s condition but also guide preventive care and restoration strategies.

Beyond degradation monitoring, FTIR facilitates organic–inorganic component analysis. By comparing the relative intensities of spectral bands, conservators can assess the ratios between binding media, mineral pigments, and past restoration agents. This is crucial for determining the compatibility of modern materials in conservation treatments and for identifying potential contaminants or prior interventions [45].

Furthermore, FTIR spectra can be collected sequentially under accelerated aging conditions to model environmental stress effects. This allows researchers to correlate chemical alterations with physical deterioration (e.g., loss of gloss, cracking), thereby providing empirical data for storage guidelines, exhibition light levels, and humidity control protocols.

Overall, the adaptability of FTIR, its broad spectral coverage, and the growing availability of lacquer-specific spectral libraries make it a cornerstone technique in lacquer conservation science. When used in combination with complementary methods—such as Py-GC/MS for molecular identification or OM/SEM for structural mapping—it significantly enhances the resolution and reliability of lacquer artifact diagnosis.

3.1.2. Raman Spectroscopy

Raman spectroscopy is a molecular vibrational technique that detects inelastic scattering of monochromatic laser light, allowing the identification of chemical bonds such as C=C stretches and aromatic ring breathing modes. This makes it particularly effective in differentiating natural lacquer binders (e.g., urushiol, laccol) from synthetic resins like phenolics or epoxies, which exhibit markedly different spectral features due to their polymer structures [46,47].

For instance, Pritchard (2024) [48] noted that natural lacquer shows a prominent aromatic ring skeletal band near 1600 cm⁻¹, while synthetic coatings often produce broader and more complex backgrounds, especially in phenolic-based systems. Sedó et al. (2013) [49] further enhanced this differentiation by using peak intensity ratios and copolymer fingerprinting, improving the specificity of lacquer identification.

While Raman spectroscopy is frequently categorized as a non-destructive technique, this classification requires nuance in cultural heritage contexts. High laser power, prolonged exposure, or dark-colored lacquer surfaces can result in local thermal damage, especially if micro-focused beams are used without cooling or control. Moreover, although sample preparation is often minimal, in practice, micro-sampling or surface cleaning is sometimes necessary to reduce fluorescence or enhance signal-to-noise ratios.

Raman’s major strength lies in its high spatial resolution, enabling detailed analysis of individual lacquer layers, interface mapping, or pigment particle identification within stratified surfaces. This makes it especially valuable in cross-sectional studies of multi-layered lacquer systems, where it complements techniques like FTIR and OM by offering localized molecular characterization without altering the sample geometry.

Raman spectroscopy offers a powerful and relatively low-impact approach to the structural analysis and authentication of lacquer artifacts. When employed with appropriate technical safeguards and in conjunction with other complementary techniques, it significantly contributes to the non-invasive, stratigraphic, and material-specific investigation of East Asian lacquer heritage.

3.1.3. X-Ray Fluorescence Spectroscopy (XRF)

X-ray fluorescence spectroscopy (XRF) is a non-destructive analytical technique widely employed in cultural heritage research for elemental composition analysis. The method is based on the principle that when a material is irradiated with high-energy X-rays, inner-shell electrons are ejected, resulting in the emission of characteristic secondary (fluorescent) X-rays as outer-shell electrons fill the vacancies. Each element produces a unique set of emission lines, allowing qualitative and quantitative determination of elemental constituents [49,50,51,52].

XRF systems are categorized into two primary configurations:

• Energy-Dispersive XRF (ED-XRF)—This method utilizes a semiconductor detector to resolve emitted X-rays by energy levels. It offers rapid analysis with moderate resolution, suitable for in situ applications.
• Wavelength-Dispersive XRF (WD-XRF)—This approach employs diffraction crystals to separate X-rays by wavelength, providing higher spectral resolution and sensitivity, albeit with longer acquisition times.

In addition, field-portable XRF (FP-XRF) devices enable non-destructive in situ analysis of immovable cultural heritage objects such as murals [53].

XRF has been widely applied in the study of lacquered objects, particularly for the identification of inorganic pigments and fillers. For example, Pitthard et al. successfully applied µ-XRF to a Qing Dynasty carved lacquer screen, identifying cinnabar and minium pigments [54]. Kamiya et al. detected sulfur (S), iron (Fe), arsenic (As), and mercury (Hg) in the sample when using XRF to detect a tray in the Kamakura-bori style [55]. Also, in the testing and analysis of the lacquer film from a Song Dynasty coffin, Wang utilized XRF to detect that the red pigment used in both the male and female coffins was mercury sulfide [51].

XRF spectroscopy plays a significant role in lacquerware and studies, particularly suitable for trace element provenance studies and surface degradation monitoring, for example, identifying corrosion products like chlorides in metal substrates beneath lacquer layers. This technique offers advantages including non-destructiveness in specific applications (requiring no physical sampling), high efficiency (real-time data acquisition within seconds to minutes), and simultaneous multi-element detection. However, it has limitations such as surface sensitivity (detection depth limited to micrometers or millimeters), matrix effects (requiring calibration to correct absorption/enhancement effects), and restricted light element detection (needing special configurations for elements below sodium). For more comprehensive material characterization, XRF is often combined with complementary techniques including FTIR, Raman spectroscopy, and SEM-EDS [49,50,51,52,53,54,55].

3.2. Chromatographic Techniques

Chromatographic techniques provide powerful tools for the precise separation, identification, and quantification of organic compounds in lacquer, particularly those that are thermally stable or bound within aged matrices. These methods are largely destructive but remain indispensable for obtaining high-resolution molecular fingerprints of lacquer components. Among these, pyrolysis–gas chromatography–mass spectrometry (Py-GC/MS) is the benchmark technique for analyzing natural lacquer materials [56]. By thermally decomposing the sample under inert conditions, Py-GC/MS releases characteristic volatile fragments that can be matched to marker compounds of urushiol (from Toxicodendron vernicifluum), laccol (from Rhus succedanea), or thitsi (from Melanorrhoea usitata) [57]. This makes it especially effective for distinguishing between Chinese, Japanese, and Southeast Asian lacquer traditions, even when the sample is severely aged or degraded. Furthermore, THM-Py-GC-MS (thermally assisted hydrolysis and methylation–Py-GC-MS) can provide the most detailed compositional information about the catechol-rich saps from the three main species of trees in the Anacardiaceae family used in Asian lacquers, as well as a wide range of lacquer additives [58].

Together, these chromatographic techniques enable researchers to discriminate between lacquer species and regional formulations, reconstruct historical recipes and material additives, and monitor chemical deterioration at the molecular level with high precision. Although these methods typically require micro-sampling, their exceptional chemical specificity and diagnostic accuracy establish chromatography as a cornerstone in scientific lacquer identification and restoration planning. When integrated with spectroscopic and microscopic techniques, chromatographic data contribute to a multi-dimensional analytical framework that supports both the technical understanding and practical conservation of lacquered artifacts.

3.3. Microscopic Techniques

Microscopic techniques are essential for visualizing the layered construction, surface morphology, and microstructural integrity of lacquered artifacts. Optical microscopy (OM) is commonly used to observe the stratigraphy of traditional lacquer coatings—typically comprising ground layers, undercoats, and topcoats—and to measure the cross-sectional thickness and distribution of these layers in a low-damage, minimally invasive manner [59]. This information is crucial for identifying historical techniques and planning compatible restoration interventions.

For higher-resolution surface examination, scanning electron microscopy (SEM) provides detailed imaging of surface cracking, delamination zones, and pigment particle dispersion at the micrometer scale. It is particularly valuable in assessing weathering damage, mechanical abrasion, and material inhomogeneity, which are often invisible under light microscopy [60]. Also, it can be used in variable pressure mode to eliminate the need to make the surface conductive by coating the samples, as such a coating would have precluded subsequent treatments [61,62]. At the nanoscale, atomic force microscopy (AFM) enables topographical mapping with nanometer precision. It has been used to assess surface smoothness, porosity, and film continuity, offering insight into the mechanical resilience and aging effects of lacquer films. When combined with elemental analysis techniques such as SEM-EDS (energy-dispersive X-ray spectroscopy) or with stratigraphic spectroscopic methods (e.g., micro-FTIR or micro-Raman), these microscopic approaches become even more powerful. They allow researchers to correlate morphological features with chemical composition, enhancing the interpretive accuracy of both degradation assessments and material identification.

3.4. Biochemical Techniques

Biochemical techniques, though relatively less common than spectroscopic or chromatographic methods, are becoming increasingly valuable in lacquer identification—particularly in cases requiring species-level resolution or non-destructive analysis. Among them, enzyme-linked immunosorbent assay (ELISA) has proven effective for detecting trace amounts of urushiol and its metabolic derivatives, enabling the differentiation between lacquer sources such as Toxicodendron vernicifluum, T. succedaneum, and Melanorrhoea usitata [63]. This level of specificity is critical for authenticating the geographic origin and botanical source of lacquer in cultural artifacts.

In addition, antibody-based molecular probes have been developed to investigate biological degradation pathways in aged lacquer films [64]. These probes help detect microbial enzymes and metabolic byproducts associated with fungal or bacterial colonization, shedding light on the biological mechanisms contributing to lacquer deterioration over time. Such insights are particularly relevant for evaluating conservation risks in humid or biodeteriorative environments.

As cultural institutions increasingly seek non-invasive diagnostic tools, biochemical assays represent a promising frontier—offering high sensitivity and selectivity with minimal sampling. When used alongside chemical and structural analyses, they provide a more holistic understanding of lacquer deterioration and support evidence-based conservation strategies.

3.5. Comparative Summary of Analytical Techniques

To facilitate a systematic understanding of analytical tools employed in the identification and preservation of Chinese lacquer,

Table 3. Comparative analysis of analytical techniques for lacquer characterization [25,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70].

Technique	Type	Sample Required	Spatial Resolution	Information Yielded	Limitations	Conservation Challenge
FTIR (Traditional) [36,38,44,45,58,65,70]	Spectroscopy	Micro-sample (KBr pellet)	Low	Functional groups, oxidation products	Destructive; provides average surface signal	Oxidation, surface aging
ATR-FTIR [37,66]	Spectroscopy	Minimal (surface contact)	Medium	Layer-specific functional group analysis	Limited penetration depth	Binder deterioration in individual layers
ER-FTIR [39,40,41]	Spectroscopy	None (non-contact)	Low	General composition on flat surfaces	Lower sensitivity to organic phases	Non-contact analysis for fragile surfaces
Raman [46,47,48,67]	Spectroscopy	Often required (focused area)	High	Aromatic markers, pigment, and binder identification	Susceptible to fluorescence; risk of local heating	Pigment identification; distinguishing synthetic/natural pigments
Py-GC/MS [58,59,65]	Chromatography	Yes (thermal pyrolysis required)	Molecular scale	Molecular fingerprint of binders, oils, additives	Destructive; requires thermal degradation	Lacquer origin, oil additives, degradation products
HPLC-MS [25,58]	Chromatography	Yes (solvent extraction)	Molecular scale	Light-aging products (e.g., azelaic acid, aldehydes)	Destructive; labor-intensive sample prep	Detecting aging byproducts like azelaic acid
OM [59]	Microscopy	Small cross-section	10–100 µm	Layer structure, stratigraphy, film thickness	Limited magnification and surface detail	Visualizing layer structure, applied sequences
SEM [58,60,61,62,68,70]	Microscopy	Coated sample (if non-conductive)	~1 µm	Cracking, delamination, pigment dispersion	Sample coating required; vacuum-sensitive	Physical instability, pigment dispersion
AFM [68,69]	Microscopy	Smooth surface	<10 nm	Surface topography, nanostructure	Time-consuming; sensitive to sample geometry; primarily used on modern lacquer films; not yet standard in heritage studies, but shows strong potential	Micro-cracking, nanostructural wear
ELISA [63]	Biochemical	Micro-sample	N/A	Urushiol species-level identification	Requires specific antibodies; library not always complete	Botanical source authentication
Molecular Probes [64]	Biochemical	Yes	N/A	Microbial degradation markers	Limited availability; often requires lab customization	Detecting microbial deterioration

presents a comparative summary of major techniques across four categories: spectroscopic, chromatographic, microscopic, and biochemical. Each technique differs in terms of sample requirements, spatial resolution, information output, and technical limitations—factors that must be balanced according to the specific needs of conservation work. For example, ATR-FTIR and ER-FTIR offer non-destructive surface analysis, making them ideal for fragile or historically significant artifacts, while Py-GC/MS and HPLC-MS provide molecular-level insights into lacquer composition and aging products, albeit at the cost of irreversible micro-sampling. Microscopic techniques such as OM and SEM enable structural observation of layer stratigraphy and surface cracking, which are critical for diagnosing degradation. Notably, although atomic force microscopy (AFM) has not yet been widely applied in the evaluation of historical lacquerware, recent studies have demonstrated its effectiveness in characterizing modern Chinese lacquer films, particularly in assessing nanoscale surface topography and layer formation. This suggests its potential as a non-destructive analytical tool in future heritage diagnostics, especially where ultrafine stratigraphic and degradation features are concerned. Meanwhile, biochemical assays—notably ELISA and molecular probes—introduce a new dimension by enabling species-level lacquer identification and the detection of microbial degradation mechanisms, which are often undetectable through purely chemical means. Overall, this multi-dimensional comparison underscores the importance of integrated, cross-disciplinary workflows in lacquer analysis, where technique selection is dictated not only by analytical resolution, but also by artifact condition, research objectives, and ethical constraints on sampling. Such integrative approaches are increasingly considered best practice in cultural heritage science, supporting more accurate diagnostics and evidence-based conservation strategies.

4. Application of Chinese Lacquer Identification Techniques in the Conservation of Cultural Relics

4.1. Case Study 1: Conservation of the B54 Japanese Armour from the Royal Armoury in Turin

Chinese lacquer identification techniques play an essential and foundational role in the field of cultural heritage conservation [71]. This significance was underscored in the conservation of artifact B54, a Japanese Armour housed in the Royal Armoury of Turin. The armour presented significant challenges, including surface delamination, pigment fading, and uncertain stratigraphy across its lacquered metal and wood components. As a culturally and materially valuable composite artifact, any intervention required high-resolution, minimally invasive diagnostic analysis to ensure material compatibility and preserve historical authenticity. Notably, its lacquer technique shares strong chemical and structural similarities with Chinese traditions, justifying the adoption of East Asian analytical models within a Western institutional context.

To address these challenges, a multi-technique analytical workflow was employed, integrating insights from Chinese lacquer identification with Western conservation protocols. Cross-sectional microscopy (OM) revealed a well-preserved stratigraphy—ground layer, undercoat, and topcoat—characteristic of traditional craftsmanship (Figure 2). This finding directly informed decisions regarding appropriate layer thicknesses and compatible materials for interventions.

Complementary non-destructive pigment analysis using X-ray fluorescence (XRF) identified the traditional red pigment cinnabar (HgS), precluding the use of chemically incompatible modern pigments that could distort reflectance or catalyze degradation. Furthermore, visual and microscopic analysis pinpointed interfacial delamination between the lacquer film and its metallic substrate (Figure 3), indicating that differential thermal expansion and humidity cycles were causing structural failure. This revealed not only the material composition but also the physical stresses inherent in the object’s composite nature, underscoring the need for adhesives compatible with both lacquer and metal substrates.

Guided by prior compatibility testing confirming no adverse reactions with the artifact’s cinnabar pigments, urushiol-type binders, or metal substrate, the interdisciplinary team selected Plexisol P550 (Rohm and Haas Company, Philadelphia, PA, USA), a reversible acrylic resin, for localized re-adhesion. This choice enabled secure re-bonding while adhering to core conservation principles of minimal intervention and reversibility.

Consequently, the conservation of B54 exemplifies the successful integration of Chinese lacquer authentication methods—specifically stratigraphic analysis, chemical identification, and compatibility testing—with ethical conservation practice. However, the case also highlights a limitation: while surface stratigraphy and pigment composition were well characterized, the long-term chemical stability of Plexisol P550 with lacquer remains uncertain, pointing to a broader challenge in conservation—balancing immediate reversibility with long-term durability.

4.2. Case Study 2: Application of Chinese Lacquer Identification Techniques in the Conservation of Ba Lacquerware from the Lijiaba Site

The discovery of a lacquered scabbard at the Lijiaba site in Chongqing, dating to the Warring States period, presented significant conservation challenges [72]. These included uncertain material stratigraphy, degradation of composite organic-inorganic layers, and a lack of documentation regarding regional lacquer formulation. As a fragile archaeological artifact representative of Ba ethnic lacquering traditions, scientific analysis was essential to characterize its construction and inform both conservation strategy and archaeological interpretation.

To address these complexities, researchers implemented a multi-technique analytical workflow based on Chinese lacquer identification science. Optical microscopy (OM) and scanning electron microscopy (SEM) revealed a clearly layered lacquer structure—ground layer, undercoat, and topcoat—confirming the traditional lacquer stratigraphy. Crucially, SEM micrographs identified hydroxyapatite particles embedded in the ground layer, indicating the use of bone-derived materials in foundational preparation, a unique practice among ancient Ba artisans (Figure 4).

Molecular-level identification was achieved using pyrolysis–gas chromatography–mass spectrometry (Py-GC/MS), which confirmed that the lacquer sap originated from Toxicodendron vernicifluum, consistent with other Chinese lacquer artifacts. Pyrolysis-comprehensive two-dimensional GC/MS (Py-GCxGC/MS) extended this analysis by identifying a broad range of polyaromatic hydrocarbons (PAHs), likely derived from plant soot pigments. These results support the presence of regionally specific recipes blending lacquer sap with traditional blackening agents (Figure 5).

Further chemical analysis using thermally assisted hydrolysis and methylation Py-GC/MS (THM-Py-GC/MS) detected fatty acid methyl esters and azelaic acid, diagnostic markers of drying oils such as tung oil. These oils were likely added to improve gloss and elasticity. The total ion current and extracted ion chromatograms provide molecular confirmation of these additives, reflecting sophisticated formulation techniques in Ba lacquer practices (Figure 6). The combination of inorganic (hydroxyapatite) and organic (lacquer sap, oils, soot pigments) findings revealed a sophisticated, regionally distinct recipe that differed from mainstream Central Plains lacquer traditions. This highlights the potential of lacquer analysis not only for conservation but also for reconstructing cultural identity.

Although no active conservation was performed on-site, the results had direct implications for future preservation. The presence of moisture-sensitive hydroxyapatite necessitates humidity-controlled storage, while the detection of blended components informs restoration material selection. The critical insight here is that preventive conservation measures, informed by microstructural and molecular analysis, can be as impactful as direct intervention.

4.3. Case Study 3: Characterization and Conservation of a Qing Dynasty Folding Fan—Collection of the Spanish Fine Arts National Museum

The Qing Dynasty folding fan analyzed in this case originates from the 18th–19th century and was likely crafted for export to the European market. As a highly composite object—constructed from lacquered paper, silk linings, mother-of-pearl inlays, and bamboo ribs—it presented significant conservation challenges. The fan showed widespread lacquer cracking, pigment discoloration, and interlayer delamination, all of which were exacerbated by environmental exposure and its delicate folding structure [73]. Moreover, the lack of documentation on material recipes for export lacquerware complicated the selection of compatible conservation materials, requiring a diagnostic approach that balanced minimal intervention with detailed characterization.

A multimodal analytical strategy was employed. FTIR-ATR spectroscopy identified urushiol-based compounds as the primary lacquer binder, confirming their origin from Toxicodendron vernicifluum. Optical microscopy and SEM–EDS revealed a “ground–undercoat–topcoat” stratigraphy and identified cinnabar (HgS) and azurite pigments. Raman spectroscopy authenticated mineral pigments, ruling out synthetic dyes. XRF scanning confirmed natural shell materials in mother-of-pearl inlays, while PLM (polarized light microscopy) identified bast fiber paper and reeled silk in the linings.

The results informed key conservation decisions: low-light display protocols for light-sensitive pigments, diluted isinglass for consolidating flaking areas, and a custom microclimate frame to prevent further delamination. However, a critical limitation was the heavy reliance on non-invasive methods. While these ensured the object’s safety, they restricted deeper exploration of degradation pathways, particularly the chemical aging of urushiol binders. The absence of more invasive techniques, such as GC-MS, limited understanding of binder variability and potential restoration compatibilities.

This case illustrates the integration of Chinese lacquer diagnostics into Western conservation, showing how cross-cultural expertise can inform tailored restoration strategies. The key insight is that conservation of composite lacquerware requires not only a layered diagnostic approach but also methodological flexibility: prioritizing non-invasive analysis for preservation, yet acknowledging its limitations and the potential need for minimally destructive techniques to fully understand degradation.

4.4. Case Study 4: Investigation of Ryukyu Lacquerwares by Pyrolysis–Gas Chromatography–Mass Spectrometry

This case study examines Ryukyu lacquerwares (17th–19th century) from the Urasoe Art Museum, integrating cross-sectional microscopy, XRF, Py-GC/MS, and strontium isotope ratio analysis using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) to reconstruct production techniques and material provenance [74].

Cross-sectional analysis initially reveals the multi-layered structure of lacquerware through sample cutting and polishing under a microscope. This method provides direct observation of the lacquerware’s surface structure, enabling the clear identification of interfaces between different materials, such as lacquer layers, pigment layers, and metallic powder layers. This technique is highly effective for revealing the layered nature of lacquerware craftsmanship, especially in distinguishing different artistic techniques, such as Sanda-e (three-dimensional painting) and Shiro-e (white painting). However, cross-sectional analysis is limited to surface observation and does not provide insight into the chemical composition of the materials in this specific case. However, if they had been analyzed using SEM-EDX, micro-XRF, micro-FTIR, or micro-Raman, these techniques would have certainly provided much more detailed information about their chemical composition. A deeper understanding of the origins and chemical makeup of the lacquer requires the application of more precise analytical methods.

Through XRF analysis, the study identified major elements in the lacquerware, such as iron, calcium, and mercury, which play a crucial role in identifying pigments and mineral components used in the lacquer. For instance, the prominent signal of mercury in the red layer confirmed the use of vermilion as a pigment. However, XRF has its limitations in that it primarily analyzes surface elements and cannot effectively detect lighter elements (such as carbon and hydrogen) or even non-complex organic molecules. While XRF provides preliminary insights into the lacquerware’s composition, it still requires complementary methods for a comprehensive understanding of the organic components in the lacquer.

Pyrolysis–gas chromatography–mass spectrometry Py-GC/MS is a key analytical technique in this study, particularly valuable for analyzing the organic components of lacquer derived from lacquer trees. This method breaks down organic molecules in the lacquer sample via pyrolysis, followed by gas chromatography separation and mass spectrometry analysis to determine their structure. The study revealed that Py-GC/MS accurately identifies enolic compounds in lacquerware, such as tricyclic enols and urushiol, which are characteristic of lacquer tree sap. This technique enabled the authors to confirm that the lacquer originated from specific species of lacquer trees (such as T. vernicifluum and T. succedanea) and to detect the presence of mixed lacquers. While Py-GC/MS provides highly detailed chemical data, the method is demanding in terms of sample preparation and analysis, requiring precise control over sample pre-treatment and pyrolysis parameters to avoid loss or misinterpretation of components.

Strontium isotope ratios (^87Sr/^86Sr) were analyzed using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), following standard procedures of acid digestion and ion exchange separation. This approach enabled high-precision isotopic profiling of inorganic components embedded within the lacquer matrix. The results revealed that some lacquers used in Ryukyu artifacts originated from mainland China, supporting the hypothesis of sustained cultural exchange and trade between Ryukyu and China during historical periods.

However, the interpretive power of strontium isotope analysis is inherently limited by the challenges of provenance attribution. Given the wide geographic distribution of lacquer tree cultivation and the coexistence of multiple species within the same region, a single isotopic measurement may not yield definitive source identification. Although this multi-technique workflow provided a nuanced understanding of Ryukyu lacquer technology, it also highlighted methodological trade-offs. Py-GC/MS, while offering detailed molecular insight, requires destructive sampling and meticulous pretreatment to prevent misinterpretation. Meanwhile, isotope ratio analysis, though powerful, may struggle to resolve overlapping regional signatures on its own. Nevertheless, the combined use of structural (cross-sectional microscopy), elemental (XRF), molecular (Py-GC/MS), and isotopic (Sr ratios) techniques established a comprehensive analytical framework, elucidating both the technological sophistication and intercultural dynamics inherent in Ryukyu lacquerware production. In contrast, the Qing Dynasty folding fan case relied on non-invasive methods such as FTIR-ATR, XRF, and SEM, which enabled the identification of pigments, stratigraphy, and organic binders without compromising object integrity. These findings informed minimal intervention strategies, including low-light display and the use of diluted isinglass for consolidation. Conversely, the Ryukyu lacquerware analysis leveraged more invasive methods—most notably Py-GC/MS—to uncover lacquer species and degradation pathways, which shaped long-term preventive measures such as humidity control.

Together, these cases underscore how analytical technique selection directly influences conservation decisions. The Qing fan benefited from rapid, surface-level diagnostics appropriate for fragile, display-oriented preservation, while the Ryukyu lacquer required deeper chemical insights to inform broader environmental management. This comparison highlights the importance of methodological flexibility in lacquer conservation, where analytical depth must be balanced against object sensitivity and curatorial priorities.

In conclusion, while this study demonstrates the power of advanced analytical techniques in lacquer analysis, future research should aim to refine these methodologies and further integrate them into standardized, multi-faceted workflows. Such approaches will enhance the precision, safety, and cultural relevance of lacquer conservation across diverse artifact types and historical contexts.

4.5. Case Study 5: Korean Lacquerware from the Late Joseon Dynasty: Conservation and Analysis of Four Objects at the Asian Art Museum of San Francisco

This case study investigates four lacquered objects from the late Joseon Dynasty—including a round table, a twelve-sided table, a tray, and a folding screen—housed at the Asian Art Museum of San Francisco [75]. A broad analytical toolkit was applied, combining optical microscopy (OM), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDX), Fourier-transform infrared spectroscopy (FTIR), thermally assisted hydrolysis and methylation pyrolysis–gas chromatography–mass spectrometry (THM-Py-GC–MS), polarized light microscopy (PLM), and X-ray fluorescence (XRF). Together, these methods offered a multi-layered understanding of Joseon lacquerware technology.

OM revealed stratigraphy and layer thicknesses, with UV illumination distinguishing subtle fluorescence contrasts between layers, such as the transition from red lacquer to orange-fluorescing underlayers in the round table. SEM–EDX confirmed the use of vermilion pigments (HgS) in red layers, along with silicon and aluminum in the ground, likely from clay or quartz fillers. FTIR spectra detected Si–O stretching bands consistent with quartz and clay minerals, as well as minor organic signals (proteins and fatty acids), suggesting the inclusion of organic binders in ground layers.

THM-Py-GC–MS provided crucial molecular insights, identifying urushiol- and laccol-based saps from Toxicodendron vernicifluum and T. succedaneum, as well as additives such as drying oils (glycerol, fatty acids), natural resins, and shellac (aleuritic acid, shellolic acid methyl esters). This confirmed both traditional sap use and later modifications with exogenous resins. PLM identified bast fibers such as ramie or hemp in textile linings, while XRF analysis of metal inlays revealed brass (Cu-Zn alloys), linking Joseon craftsmanship to earlier Goryeo traditions.

Despite these valuable results, several limitations emerged. First, the study paid limited attention to aging processes such as oxidation, polymerization, and degradation of lacquer, which are crucial for conservation strategies. Second, the dataset was restricted to four objects, limiting the ability to generalize across different Joseon production centers or chronological phases. Third, while SEM–EDX mapping provided elemental distributions, its resolution was insufficient for detecting micro-scale variations, and FTIR did not fully probe deeper polymeric transformations within aged lacquer films.

The integration of organic (THM-Py-GC–MS, FTIR), inorganic (SEM–EDX, XRF), and structural (OM, PLM) analyses enabled a comprehensive reconstruction of Joseon lacquer technology, revealing deliberate combinations of native lacquer sap, imported additives, and textile or metallic inclusions. The detection of shellac, in particular, suggests adaptation to new materials and possibly responses to foreign market demands during the late Joseon period. These findings not only illuminate material practices but also highlight the fusion of traditional Korean craftsmanship with evolving global influences.

This case exemplifies how advanced analytical methods can transform descriptive artifact studies into critical syntheses that reveal technological choices, material challenges, and conservation needs. Future work should expand the sample base across different periods and object types, and employ higher-resolution or non-invasive methods (e.g., micro-FTIR imaging, synchrotron-based XRF) to address gaps in understanding aging and micro-scale material interactions.

5. Research Limitations and Future Directions

Despite significant advances in analytical techniques, the characterization and conservation of Chinese lacquer artifacts still face several key limitations. Most high-resolution methods—such as Py-GC/MS and SEM–EDS—require destructive sampling, which poses ethical challenges, especially for ritually significant or fragile cultural relics. Non-invasive alternatives, like ER-FTIR or handheld XRF, offer limited chemical specificity, especially for trace organic phases such as drying oil byproducts or microbial degradation markers. Furthermore, results are often fragmented across studies due to the absence of standardized protocols and spectral libraries, limiting cross-comparability.

Looking ahead, future research should prioritize not only technical refinement but also the standardization of emerging tools such as hyperspectral imaging and AI-based microstructure recognition. Hyperspectral imaging, despite limitations in lacquer reflectivity and resolution, holds promise for non-invasive pigment mapping and layer distinction. We suggest establishing a pilot framework that integrates VIS–NIR hyperspectral data with structural imaging (e.g., OCT) to build stratigraphic models and monitor surface aging indicators like micro-cracks or pigment migration.

In parallel, AI-assisted image recognition—particularly convolutional neural networks (CNNs)—has been preliminarily applied to lacquer cross-sections for automatic stratigraphy recognition. A standardized pipeline that trains CNNs on annotated lacquer micrographs, possibly fused with spectral and elemental datasets, could provide real-time diagnostic support. Over time, this framework could evolve into predictive tools that model degradation pathways and recommend preemptive conservation actions.

To support this vision, collaborative efforts are needed to develop open-access lacquer imaging datasets and training repositories. Interdisciplinary dialogue between data scientists, chemists, and conservators will be essential for embedding these technologies into conservation workflows in a replicable and ethically sound manner.

6. Conclusions

This comprehensive review establishes Chinese lacquer identification techniques as indispensable tools for cultural heritage conservation, integrating material science with traditional craftsmanship through five representative case studies spanning different historical periods and object types. These cases—from the B54 Japanese armor and the Ba lacquered scabbard to Qing export lacquerware, Ryukyu objects, and Joseon Dynasty furniture—demonstrate how multi-technique analytical strategies can move beyond descriptive study to critically address conservation challenges, such as stratigraphic uncertainty, pigment degradation, and intercultural material exchanges.

The research demonstrates that multi-technique analysis—combining stratigraphic microscopy, spectroscopic methods, and advanced chromatography—provides crucial insights into lacquer composition and degradation while revealing the need for standardized protocols and non-destructive innovations. Comparative analysis across cases further highlights how technical results directly inform conservation decision-making, from adhesive selection to environmental controls, while also exposing current limitations such as insufficient understanding of long-term aging and the ethical challenges of sampling.

Key findings highlight both the successes of current methodologies in preserving lacquer’s material integrity and the urgent challenges requiring interdisciplinary solutions, particularly in developing hyperspectral imaging, bioinspired consolidants, and predictive aging models. Future progress will depend not only on technical refinements but also on the establishment of shared international databases and reporting standards, ensuring that knowledge gained from individual projects contributes to a broader, cumulative framework. Ultimately, this systematic approach not only safeguards East Asia’s lacquer heritage but also offers a transferable paradigm for global conservation practice, balancing scientific rigor with cultural sensitivity to ensure these artifacts endure as testaments to historical artistry and technological achievement.