It has been suggested the fabric layers were bonded using animal glue.
In those times (mid 19th century), animal glue likely had been used to join the bridge onto the soundboard.
It is typically used without the addition of animal glues.
Egyptian records tell that animal glue would be made by melting it over a burning fire and then applied with a brush.
It shifted its focus from stenciling to selling animal glue to local box makers and other needs.
Factories now produce other forms of adhesives, as the process for animal glue is complex and tricky to follow.
Recently, animal glue has been replaced by other adhesives and plastics, but remains popular for restoration.
Most animal glues are soluble in water, useful for joints which may at some time need to be separated.
Most inksticks are made of either pine or oil soot combined with animal glue.
Horse hooves can also be used to produce animal glue.