What is Urushi?
all you need to know about Japanese Lacquerware
Urushi is a marvellous material with outstanding properties, but also calls for particular care and knowledge in application. Urushi lacquering is a skill deeply connected to the Japanese culture and requires a lot of training to be mastered. It should be handled with an open mind and the respect it deserves.
It also contains Urushiol, which causes contact dermatitis to most people and should be used very carefully and always handled with gloves, unless you can be completely sure that you are lucky enough not to react to it.
What is Urushi lacquer?
It is the natural, organic sap derived from the Urushi-tree (Toxicodendron vernicifluum), which grows in the monsoon areas of East- and Southeast Asia. Urushi has been used for over 8000 years and its qualities make it stand the test of time, with 2000-year-old intact pieces having been found. Fully cured Urushi can resist contact with alkali, acids and alcohol and withstand temperatures of over 300° Celsius.
What is Urushiol?
The main constituent of Urushi (up to 80% in Japanese Urushi) is Urushiol, which can also be found in poison oak, poison ivy or poison sumac and which makes it so risky if not handled correctly. The contact with the uncured sap creates ‘urushiol induced contact dermatitis’ which in short is vers nasty itchy rashes, inflammation and sometimes blistering. Since the inflammation is considered an allergic reaction it is possible to be immune to it or to gain immunity, but the latter requires years of practice and constant exposure. However, there is nothing to worry about fully cured urushi. The chance of urushied products causing a rash to people that are particularly sensitive is exceedingly small and even diminishes over time. Therefore it is very important to give your lacquered objects enough time to cure, even if it may take months.
Is Urushi foodsafe?
Yes, fully cured Urushi is perfectly food safe. Once cured, the lacquered surface is waterproof, can withstand alcohol, alkali, and even acids. Urushi has been used on tableware for centuries, due to its strength and resistance and is famously used on Japanese rice and miso bowls.
How is Urushi made?
Urushi is harvested when the tree is about 15 years old, although the older the tree, the more sap it produces. The harvesting time is from around June to October with the qualities of the sap gathered varying strongly in each month. For example, the sap gathered from June to the beginning of July has high water content and is called hatsuyama, whereas the sap gathered in September is called atogama and due to its lower water content is mostly used for base coating. After sap collection, the trees are mostly cut down, but a new tree will grow from the root system. The amount of sap collected in one season really depends on the size of the tree but for a tree of about 20 centimeters in diameter, the total amount produced is about 200-250 grams, thus making urushi a very valuable material. In fact, in the past, the cultivation of lacquer trees has been a matter of law. Nowadays most of the urushi lacquer used is coming from China, as the process of harvesting and growing urushi trees is a lot of work, and production in Japan has decreased a lot in recent times.
Ki-urushi (raw urushi) is the most natural form, which, after being filtered from impurities, is ready for use. For other types of urushi, which can be applied in thicker layers, the sap has to undergo an extended process including heating to minimise water content. In further steps pigments can be added to produce coloured urushi, red and black probably being the most common. In Japan freshly collected sap is dark brown, black is artificially created by adding iron or Sumi (Japanese black ink), whereas Urushi from other places in Asia can naturally be black in colour.
how does Urushi “dry”?
uncured Urushi right after application
Opposite from what one might assume Urushi won’t harden in dry air, but it will in a moist environment. Actually, it is not drying in the conventional sense, but curing due to a chemical reaction. When exposed to high humidity levels of about 70 - 85 %, an enzyme called laccase inside the Urushi starts acting as a catalyst for the oxidation of the material. The Urushiol content then absorbs oxygen from the humid air and polymerises, forming a hard film. Much like applying oil to woodenware, if the lacquer is applied too thickly the surface will harden, but underneath it will remain liquid, so it must be applied in very thin coats. Not only the humidity plays a role in this process, but the temperature is also very important. Urushi cures between 4-40° Celcius, with the curing process being faster, the higher the temperature. Between 40-80° C it stops curing completely but can be hardened with a special process called koonkoka-ho (high-temperature hardening process) at 100-120° Celcius. In this high-temperature process, other than the low temperature, no humidity is needed. The “drying” is controlled through a special cabinet, called the Muro, in which the urushied pieces are placed. This is typically a wooden cabinet sprayed with water from the inside. The humidity level has a great impact on the glossiness of the Urushi-finish and has to be controlled very carefully. In most cases, Urushi will dry in 5-6 hours, but it really depends on place and season. In ideal surroundings, like the warm and humid rainy season in Japan, Uruhsi can cure in 30 min, but it is typically left in the Muro for about 3 days, after the application of each layer. Since a nicely crafted urushi bowl can have up to 30 layers applied to it, this process takes a very long time. When applying the last layer to the piece, it is then placed in the curing cabinet for another 30 days to assure that the urushi has completely hardened, since it can still cause a reaction to very sensitive people, if not entirely cured.
fuki-Urushi method
cleaning the brush with Urushi before use
Urushi lacquering is a specialized craft in Japan with a very long history and many regional differences in style and method. There are various ways of applying an Urushi-finish to an object and even more ways of decorating those with materials like gold and silver dust, seashell, metal leaf, etc. Since it is possibly the easiest application technique I will explain in short the process of applying ki-Urushi (raw Urushi) to a wooden surface with the fuki-Urushi method (wipe-off method). When applying Urushi make sure to be in a dust-free environment. Ki-Urushi is very delicate and any traces of fingerprints, water, grease, salt, etc. on the piece will not make it cure properly, so it is important to thoroughly clean the piece before applying any lacquer. Before use, the Urushi should ideally be filtered through a piece of paper or small mesh fabric, to produce an even liquid. Then use a brush to apply an even coat of lacquer to your wooden piece. The first coat of lacquer can be mixed with Turpentine to make the penetration of the wood easier. The traditional brushes for this are made of human hair and are therefore very strong but incredibly expensive. Allowing the wood to rest for a few minutes after application will make it soak up more lacquer, which results in a stronger, but darker piece. The urushi then is wiped thoroughly with a cloth and worked into the wood to ensure that it has been applied evenly and to take off any excess material. Now the piece is placed in the Muro and allowed to cure. When fully hardened, the surface is sanded with high grit sandpaper or a piece of charcoal. For bowls and spoons, this procedure is repeated 5-7 times. This technique is great to bring out the gentle beauty of the wood grain while still protecting the piece with an Urushi-finish.
How do I take care of Lacquerware?
Urushi is very resistant but has one downside; it doesn’t like UV light. Long periods in sunlight or other ultraviolet light sources can cause discolourations, cracking and deterioration of the surface lustre and your pieces should therefore be stored in a dark place when not in use. To make sure your pieces keep their beautiful surface, wash them with a mild detergent and a soft sponge or cloth. Placing Urushi-ware in a dishwasher or Microwave is not recommended, as well as exposing them to extreme heat or open flames. Urushi itself can withstand very high temperatures but it is often applied to a wooden base, which may crack under high heat or rapid temperature changes.
