One of the main attributes of hide glue which is worth mentioning is
that it does not stain timber, particularly oak.  I mention this as
during my apprenticeship as a carpenter and joiner only hide glue was
used when oak was needed for joinery.

I particularly remember the very special staircase made for Bud
Flanagan's house, with very large bullnose steps at the bottom which
were about 8 feet across.  These were successfully glued without any
staining and the finished effect looked very good.

The same attributes will apply when oak is used in mechanical musical
instruments.  Other glues have been known to stain badly on the
surface, which can show up very badly after polishing.

My main recollection about the glue was keeping it at exactly the right
temperature, which, as an apprentice, was my job on pain of death if I
did not get it right!

Malcolm Cole, the Player Piano Group
London