If what you require is to stick the lens (a heart-shaped mounting piece) on the back plate (just brush a circle of paste about 1.5 cm wide around the lens) and then insert it into the frame, then this mounting is the most authentic, and it is easy to fall off when uncovered. If it is not worth collecting calligraphy and painting, use ordinary glue.
Papering is to wash out gluten and paste it with the remaining starch. And master the heat, mix water and stir, just like breaking eggs. If you haven't done it, ask the framer. You don't use it much. Just give a little to the paperhanger, all of it.