Sumac will cause effects, more or less similar to poison oak or ivy. There seems to be few younger people willing to carry on the tradition, too many less than traditional materials, that can be substituted.
The fact of skin issues related to urushi is quite well know in Japan, however with the collapse of the "lifetime"employment system and the advent of more an American style system of temps and part timers, read no benefits, many younger folks are turning to work which they feel is "real" ie. the crafts. This is similar to the recent boom in minka (traditional Japanese farm houses) restoration, this, coupled with the fact that many smaller towns have suffered from an exodus of younger people are now providing free or low cost housing to folks who are interested in settling there and carrying on a tradition. There has been a sea change concerning how folks want to/choose to live which I predict will wash ashore here in the near future. For a number of reasons over the past 10 years or so, I've thought, if you want to see the future, look at Japan. However, the 21st century is China's most likely.......
Traditionally the gold would have been powdered and no sealers would have been used. The use of epoxy and composite metal leafs (not gold) might be the reason for the need to seal.
See above, "Now a days........."
Apologies for rambling on.....
R