If anyone is curious and near South Kensington, there is now a little exhibition on urushi at the V&A [1], which includes a film of a guy who harvests his own sap, processes it into lacquer, and then makes things with it.
That video is not online AFAICT, but there is another one about another artist, which includes some footage of an urushi workshop preparing the stuff, and her using it: https://www.youtube.com/watch?v=xeult7lZtbg