Lacquer

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Lacquer is a type of "reactive finish", a term referring to an organic coating which hardens by an irreversible chemical reaction, producing a hardened film through the polymerization of a monomer or the cross-linking of a polymer, in addition to solvent evaporation. Lacquer can be divided into several categories, with two main distinctions: Asian lacquer, most notably urushi, and European lacquer, often referred to as japanning. This page primarily discusses Asian urushi and related plant-based lacquers. For more information on japanning and other artificial finishes, see varnishes.
==Materials and technology==
===History ===
====China and Japan====
The use of lacquer as a protective finish and decorative art was developed in China, and lacquered wooden objects dating to Neolithic period civilizations in China and Japan are known. A bowl from the Che-chiang province dated to approximately 4000-5000 BCE is considered the oldest extant piece of lacquerware (Kopplin 2002:19,133). The term “lacquer” results from a European misunderstanding of the nature of Asian lacquer and was derived from the Indian Sanskrit word for “100,000 lakh”, which describes the many Lac insects used to make shellac (a different finish).
====Southeast Asia====
Lacquer is known as Najeonchilgi in Korea, sơn mài in Vietnam, and thitsi in Burma. 
====European Lacquer ("Japanning")====
Lacquer objects were exported to Europe in the mid-16th century, and became prized for their unique beauty. Unfamiliar with the technology of Asian lacquers, Europeans began to integrate portions cut from Asian lacquer objects into their own furniture and crafts. In an attempt to imitate the luster and look of Asian lacquer, European workshops developed highly complex varnish mixtures using various resins and oils in multiple layers. This craft became known as japanning. 
===Materials ===
Asian lacquer is produced in East and Southeast Asia from the sap of a number of species of trees within the Anacardiaceae family, resulting in multiple sources and types of lacquer across the continent. The resin, secreted from cuts in the bark of the tree, is collected, filtered and used as a paste, primer, glue, or finish. , These trees are close relatives of poison ivy and their sap is highly toxic. The initial stages of lacquer production are similar throughout Asia, but the subsequent processing, additives and application can differ significantly between regions and cultures (see Technology below) (Kopplin 2002). 
Crude lacquer is collected by extracting the viscous sap by creating incisions into the trees. The lacquer tree can be tapped ranging from once every 3 days to once a year, depending on the species of tree and the region where they grow. Lacquer tapping is a laborious and dangerous job that starts before sunrise as it can dry up quickly. Generally, a lacquer farmer can collect an average of 800 grams of raw lacquer by tapping 300 to 400 trees a morning, as each tree only produces 1-5 grams of raw lacquer every other day. 
In contrast, European japanning utilized many different tree resins including colophony, sandarac, and copal, as well as resins from insects, like shellac. Organic colorants such as gamboge and dragon's blood were used to imitate the characteristic Asian designs and colors. Drying oils were added to regulate the drying process. These materials were dissolved in organic solvents and applied in layers, which were buffed to a high gloss. This process illustrates an important distinction between Asian lacquer, which forms through solvent evaporation and polymerization, and European japanning, which forms primarily through solvent evaporation.
====Japanese Urushi lacquer====
Urushi is the latex resin or colloidal sap of a small tree from the Anacardiaceae family (Rhus genus, Vermiciflua species) and has been used as the primary source of lacquer in both Japan and China. Raw urushi is an oil-in-water emulsion and dries by solvent evaporation and polymerization. The uncured monomer contains urishiol and the enzyme lacase, which are responsible for the hardening reaction. Cured urushi is a cross-linked phenolic (cyclic) hydrocarbon with a structure similar to contemporary plastic network polymers.
====Chinese lacquer====
Traditional lacquer in China is known as qi, and is also produced from the sap of trees in the Anacardiaceae family.
====Southeast Asian lacquer====
The variety of Southeast Asian lacquers consist mainly of the sap from trees within the Anacardiaceae family. Thai lacquer is produced primarily from the sap of Melanorrhoea trees, a member of this family. The Vietnamese lacquer tree, known as cây sơn ta, is Toxicodendron succedaneum and is primarily found in the Northwestern region of Vietnam. 
===Technology ===
====Japanese Lacquer Techniques====
The highest quality urushi was tapped directly from trees, while the lower quality was boiled out of the cut-up branches of trees already exhausted by tapping. The sap was then concentrated by boiling to yield a viscous product ready to apply to a substrate, or mix with other materials, such as flour or clay, to form a ground (Thornton 2008), (Webb 2000). 
Common substrates used for lacquer in Japan are the wood of the hinoki (Japanese cypress) tree, the elm, and quince trees. Metal was often used as a base for lacquer, especially in armor. Frequently an organic layer was used between lacquer and metal, making the finished object particularly sensitive to fluctuations in relative humidity. A variety of other substrates known include, bamboo, fabric, paper, leather (shipi, shaped rawhide used in Japan), and ceramics (only in the earliest known examples (3000 – 2000 BCE, and in the last 100 years used only as a repair method). Organics, such as gourds, ivory, bone, tortoise-shell, horn and shell were incorporated as decorations (Webb 2000). 
Various grounds have been used for Japanese lacquer, depending on the desired quality of the final product. The highest quality ground used was fairly pure urushi mixed with tonoko (powdered earthenware pots) to form sabi, a grey colored paste. Nikawa is a less expensive, reddish brown colored ground, made with animal glue and treated with formalin to become insoluble. Nori or rice paste was mixed with tonko for the cheapest goods and is also red-brown in color. Pigblood is a ground made of clay, pigblood and Pauolonia oil (used also in China). Polyvinyl chloride (PVC) is the cheapest and most common ground for modern lacquer, a black plastic that is decorated with a final few layers of urushi (Webb 2000). 
Lacquer is applied in multiple thin coats, often more than 20, with each subsequent application first dried at high humidity, and then in ambient air. The grade of lacquer chosen was determined by the objects intended use and often different grades of lacquer were used together for separate components of one object. Color was imparted by adding mineral and/or organic pigments. Few pigments are compatible with the lacquer emulsion and so colors of lacquer are limited. Cinnabar (red), orpiment (yellow-orange) and black (iron oxide) were the most common pigments used and were mulled into the lacquer, similar to the oil paint-making process. 
Specific terms for Japanese decorative lacquer techniques: 
:Hiramakie (low relief): the design is contained in one lacquer layer that stands up very slightly above the polished but undecorated surface. 
:Takamakie (high relief): the design is made with multiple lacquer layers, creating a sculptural effect. 
:Todigdashi makie: the design is covered with lacquer layers and the surface is polished completely smooth (Thornton 2008).
====Chinese Lacquer Techniques==== 
Carved lacquer – multiple layers of lacquer carved in elaborate designs. Arguably the most important lacquer technique from China, often bright red, colored with cinnabar.
:Chui-hua (needle painting) - Engraved designs into the covering coats of lacquer with needle-like gouges, developed in the Han period.
:p'ing-t'o (shallow scooping) - Expensive technique of arabesque filigree, influenced by Persian styles, developed in the T'ang period. (Kopplin 2002: 25-45)
====Southeast Asian Lacquer Techniques====
Lacquerware in Thailand can be classified into two groups, according to ethnic origin: 1) the designs of the Authaya and Bangkok cultures, distinguished by the use of gold on black backgrounds and mother-of-pearl inlay; and 2) the designs of the Lanna, a northern Thai culture, with a common color scheme of red on black (Kopplin 2002:133-141).
In Vietnam, raw lacquer is filtered and processed before it is sold and used by lacquer artisans. Refining raw lacquer involves stirring and kneading, which will reduce the water content of the resin and give it slow curing time and gloss. Harvested raw lacquer is stored in containers to separate different grades of lacquer. Sơn mặt dầu, also known as lacquer oil, contains the highest concentration of solids and almost no water, making it impossible to cure. It is often used for final polishing or added to lower-grade lacquers to improve overall quality. First-grade raw lacquer, with high laccol content and minimal water, is reserved for painting work. Second-grade lacquer contains higher water content and gum, making it a fast-drying lacquer suitable for foundational work or as boat varnish, as well as a very strong natural adhesive. The raw lacquer is then refined by stirring to reduce water content, thereby improving glossiness, working time, and transparency.
===Deterioration===
When new, lacquer is extremely durable, waterproof and insoluble in virtually all organic solvents. However, its strength is fugitive, and it will invariably degrade with age, eventually becoming soluble in water and other polar solvents. Despite its initial strength, severely deteriorated lacquer can even be permanently etched by fingerprints. 
As the lacquer films are first cured in high humidity, the dried film contains 3% bound water and other hydrophilic compounds. The desiccation or loss of this water can lead to the breakdown of the lacquer film, making the control of relative humidity (RH) in the storage environment important (Webb 2000).
Extended exposure to light will cause irreversible deterioration to the lacquer surface, resulting in a noticeable decrease in luster and vibrancy of color. It is important to note however that the surface of light-damaged lacquer may become soluble in water or other solvents even before physical changes are readily apparent. Any aqueous cleaner should thus be tested in areas that have received the maximum amount of light exposure.
==Conservation and care==
 This information is intended to be used by conservators, museum professionals, and members of the public for educational purposes only. It is not designed to substitute for the consultation of a trained conservator.
*To find a conservator, please visit AIC's Find a Conservator page.
Compositional distinctions and technological differences between Asian and European lacquers affect their physical properties, aging behaviors and inherent stability. All of these factors ultimately impact any decisions regarding preventive care or necessary conservation treatment.
===Documentation ===
For examination or documentation of issues specific to this material, including tips for accurately and meaningfully documenting specific materials, common types of previous repairs or restoration, etc. For general recommendations, please refer to the Objects wiki article on Conservation Practices or for general conservation work practices, please refer to the main AIC wiki section on Work Practices.
===Preventive conservation===
Lacquer is easily damaged if stored in improper conditions of light and relative humidity. It is recommended that all lighting equipment should have UV radiation filtered. Recommended parameters for display are 50 Lux or 5 footcandles, with a maximum exposure time of 6 months over 5 years (Smithsonian NMAA 2024) . 
===Interventive treatments===
There are many considerations in the approach to conserving Asian lacquer, including thickness of ground, binder of ground, the number of layers of lacquer, its state of degradation and type of deterioration. Due to the layered nature of lacquer, the layer which requires treatment must first be identified. 
As noted above, the surfaces of degraded or light-damaged lacquer may become soluble in water or other solvents even before physical changes are readily apparent. Any cleaning solution should thus be tested carefully.
An interesting debate that often arises in the conservation of Asian and Japanese art, including lacquer, is the treatment approach and the difference between traditional repair methods and western conservation ethics. In Japan, urushi is often used as a consolidant. However, this method is not reversible or distinguishable from the original surface. A conservation treatment intended to make the object re-treatable would most likely employ a reversible consolidant (Webb 2000).
==References==
: Brommelle and Perry eds. 1988 Urushi Proceedings of the Urushi Study Group June 10-27, 1985 Tokyo, The Getty Conservation Institute, printed in Tokyo Japan.
: Budden S., Halahan F. 1994. Laquerwork and Japanning Postprints of teh Conference held by UKIC at the Courtauld Institute of Art in London, May 1994, Hobbs The Printers Ltd, Southhampton, England.
:Kopplin M. 2002. Lacquerware in Asia, Today and Yesterday United Nations Educational Scientific and Cultural Organization, Paris.
: Thornton J. 2006. Unpublished class notes, Art Conservation Department, Buffalo State College State University of New York.
:Webb M., 2000. Lacquer Technology and Conservation Butterworth-Heinemann, Reed Educational and Professional Publishing Oxford UK
: Characterization of Asian and European Lacquers Getty Conservation Institute, Current Projects, last update 2010
==Further reading==
The Getty Conservation Institute: The Characteristics of Asian and European Lacquer
Lacquer: The Bishop Museum, Art Conservation Handout
Urushi and Conservation: The Use of Japanese Lacquer in the Conservation of Japanese Art
 The Conservation of Asian Lacquer
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