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.