Black lacquer is a refined lacquer with color added, it has similar urushiol and water content to red lacquer if it is a top black, if it is a middle black the content may be slightly lower. Top and middle lacquers are just as they sound, top are of sufficient quality to be used as a top, exposed coating, middle lacquers are of a quality that they require a top layer of lacquer to cover them.
The schedule for tapping lacquer is very detailed, running from June – November and involves starting on the sunny side of the tree close to the ground and slowly moving the score marks around and up the trunk. The final stages of harvesting involve chopping the tree down and splitting the limbs to scrape out the lacquer. This final procedure gives an especially strong adhesive lacquer called seshime. The quality and amount of sap obtained is dependent on the person doing the tapping. The new tree will sprout from the stump.
The schedule below is from a manual on tapping.
Middle of June to middle of July. Hatsuurushi Tree is slightly scored, flow is minimal.
Middle of July to third week of August. Moriurushi. This is when the best quality sap is collected.
Middle of August to third week of September. Osourushi and/or urame, tome, and edaurushi.
Middle black lacquer is used over both sabi, (jinoko or tonoko/lacquer mix) and mugiurushi, (flour/lacquer mix) as a layer to give you a smooth finish. Without a middle layer of lacquer it is very difficult to get a smooth enough finish to successfully apply a top layer of lacquer and then metal. Middle lacquer is not as hard as top lacquer.
Red lacquer is a refined lacquer, much more so than basic lacquer. It is about 75% urushiol compared to basic having about 60%. The water content is about 15%, compared to about 30% for basic. The urushiol contains an enzyme called laccase which is the catylist for converting the lacquer into a natural polymer, combining with oxygen in the humid and warm air of a drying box. If the temperature is too warm the laccase will ‘die’ and the lacquer won’t cure.
95% of the lacquer used in Japan is manufactured in China. Japanese made lacquer is of a much higher quality and is far more expensive than Chinese, at least double the price, often times 4 times more expensive.
Lacquer is a difficult and complicated medium to use and understand. In addition to different names for the same lacquer there are regional names used along with names that differ for the same lacquer depending on the trade it is used in. I know of at least 64 different types of lacquer and of those 15 are basic types.
Red lacquer is used in kintsugi for a substrate for metal. It is a good quality lacquer that can be polished out to a high sheen and is harder than middle lacquers.
Kiurushi, basic lacquer.
Basic lacquer has many names, one is kiurushi. It is about 60% urushiol, the active ingredient that is responsible for both the skin reaction some people experience and contains the enzymes that are active in the 25C-38C temperature band along with at least 75% humidity to form a natural polymer. Lacquer is collected from 10 – 20 year old lacquer trees that are tapped once with part of the processing involving cutting down the tree. That is to say, lacquer comes from a tree that is only good for 1 tapping and then cut down, yielding about 200 cc of liquid. Kiurushi is that liquid with the only processing being that it is stirred and slightly heated.
It is possible to only use kiurushi for all the steps of kintsugi excepting advanced metal work.
Below is the general description of basic lacquer.
There are several types of lacquer you use in kintsugi. This post is on the basic lacquer called kiurushi. Kiurushi is used in most of the basic steps of kintsugi. For sticking pieces back together you mix it with flour or rice, to do fill work or to do restorations you use it and mix it with either jinoko or tonoko to make a mixture called sabi. If you are doing a repair such as fixing a blistered glaze you would use this lacquer too. I don’t use wood powder but if you did you would mix it with kiurushi. It comes out of the tube a brown milky color and as it drys it turns black or a very dark brown. It can cause skin rashes but doesn’t seem to do so with everyone. I get rashes but most of the people I have had in workshops have never gotten a rash despite having direct contact with it. Like all real lacquers it requires a damp and warm environment to dry properly, it won’t usually cure in a normal environment.