Rum
Note that the polymerizing part of traditional cashew lacquer is also urushiol. This is why you can't buy entirely raw cashews, they can have enough of the annoying stuff to cause some people to react, but with heat and moisture it cures out. The bottom of the cashew apple where the nut is is basically a little sack of urushoil resin (a smidge less pure than the urushi plant but much moreso than say poison ivy).

It's also in Mango sap FYI, some people will break out horribly from handling them, moreso if they're green.

I have no idea how the lacquer you have is made/treated so it might be treated to remove the reactivity.. I believe some types are/were not but ?most? are I believe at least air curing (assuming sufficiently thinned coats perhaps?). But I might exercise some caution to ensure that it is adequately cured before handing it off to the less fortunate or indeed shaking their hands after you've been finger painting it on You might also appreciate that sensitivity can be acquired, so enjoy your lack of suffering while it endures