making parchment glue

Cennino Cennini's (c.1370-c1440) traditional recipe: gently boil the proportion of one ounce of parchment scraps in a gallon of water for four hours. spread the resulting gelatin onto a glass plate, and dry in open air. The flakes can be used as normal hide glue, heated.
I use this method for making the glue for the parchment roses, having experimented with isinglass, hide, rabbit skin, and even synthetic glues without acceptable results.
Cennini was an italian painter, who wrote in the early fifteenth century (speculative date) Il libro dell'arte, a compendium of renaissance techniques for painting and preparing materials.

The finished sheet of glue, after drying