Animal Hide Glue - 'Secrets'

Hi All,  I hope Robbie or whoever edits this posting will leave the
Subject intact as it is written.  This is because I really hope we can
learn some secrets about animal hide glue.

A customer who had purchased some hide glue from me wrote:

  "Your shipment arrived, perfectly intact, this afternoon.  Thank you
for enclosing instructions, as I am a hide-glue novice (I have glued up
one set of bellows, with much cursing and gnashing of teeth).

  "But, also, I am something of a Luddite (and don't have a fancy
'lectric glue pot), so I am curious how craftspeople heated glue and
judged temperature in the days before electricity.  It seems to me that
a little charcoal hibachi would work for heat--although I suppose they
had wood stoves in their shops and knew the perfect spot on or near it...

  "But it seems to me that the glue itself should indicate correct
temperature by some distinctive change in physical behavior or
appearance--some way it drips off the brush or puddles up or feels when
one rubs it between ones fingers.  Well, I suppose I can experiment."

I told him I would look into the matter because I couldn't give him
a direct answer.  When I started using animal hide glue, all I had was
a candy thermometer, a glass jar, and a double boiler.

So, since animal hide glue has been around for thousands of years,
how did the ancients know when the glue was at the "right" temperature?
Or did they even care?

I would imagine that the people who knew the "secrets" of making good
hide glue for putting together furniture were highly respected.
Imagine a Roman king sitting down on his throne one day, and it falling
apart.  You can bet there would be one less subject in the kingdom.
And knowing that was a very real possibility, who had the guts to make
the king's furniture if he wasn't sure it would stay together for at
least 'his' lifetime?

Personally, I've never studied hide glue from the standpoint of not
having a few basic tools (thermometer, double boiler, and glass jar),
and some basic knowledge, like the ratio of glue crystals to water to
start a batch.

It also dawns on me that the ancients probably didn't have glue
crystals.  They most likely rendered down the animal parts until they
got sticky.  And, come to think of it, how did they ever figure out
that animal parts could be rendered down to make a glue?  I can't
imagine someone setting out to make a glue, and coming up with the idea
of using left over animal parts.  So, it must have happened sort of by
accident.  (Another 'Secret'.)

In closing, if anyone can shed some light on this matter, I would be
most appreciative.

Musically,
John A Tuttle
Player-Care.com
Brick, New Jersey, USA