Thank you for the detailed reply, that is very interesting! In the 1960's I built model airplanes and applied the decals just as you describe. They were certainly thin and delicate and I remember ruining a few with clumsy handling.
I recall these were sometimes referred to as decalcomania, so I looked it up:
decalcomania de·cal·co·ma·ni·a (/dēˌkalkəˈmānēə/) noun: - 1. the process of transferring designs from prepared paper on to glass or porcelain. 2. a technique used by some surrealist artists which involves pressing paint between sheets of paper.
If I understand
Johnny Best's description correctly, the paper is like today's "release liner", the layer of water-soluble glue from the coated paper adheres to the first layer of varnish ink which together become the "adhesive-coated substrate", the colored ink layers are the "printed graphic", and the final layer of varnish ink is the "over-laminate"!
Hmmm.... so is varnish-ink-varnish on the same water-soluble-adhesive coated paper substrate something which is or could be done with latex or UV ink using today's digital printers?
"It seems like the more things change, the more they stay the same." -- unknown