I have learned some things regarding hot hide glue recently that I
thought I'd pass along.

    I buy my hide glue in 100# bulk from Milligan and Higgins. Up until
now, I had assumed that the quality of all hide glue was generally
mediocre, but usable. It never really passed the cold water test I
have made on samples, assuming that was the best available. Here is
what I would do:

    I take a tall tumbler, as narrow as possible, and dump a small
quantity of glue crystals into it. You can weigh them if you wish. I
like to fill the bottom 1/5th with dry crystals. Then I add cold water
to it and wait, overall, twelve or more hours. But within a few hours'
time, the proteins and fats in the glue are beginning to separate. The
poorer the quality of glue for woodworking, the weaker it will be. You
tell this by both how fast it separates as well as the degree it
ultimately separates. You will have a lot of "slime" above the glue
lump in the bottom after twelve hours or more. Pour it all off, and
weigh the lump in the bottom. The best glues will take up 3-5 times
their weight in water and will be a solid and cohesive mass that has to
be "scraped" out of the glass. [So it is better to weigh the dry glue
and glass together to begin with, after you have first weighed the dry
glass, and subtract.]

    The lighter proteins in glue float at higher levels in the water.
The lighter the protein, the weaker the glue. Very light colored glues,
called "high clarity" or "technical gelatin" are usually weaker glues
as well. The lighter color does not indicate a "pure form" of hide
glue. So unless you are planning on flavoring it vanilla, I wouldn't
look at crystal color as an indication.  Granted, these glues are still
strong enough for player work, but if you ever had to repair a broken
Knabe grand lid, for example, I wouldn't recommend them.

    The bad smell from glue comes from the putrefaction of fats still
in these glues. You will find that the better the glue tests, the
smaller the percentage of fats and the longer its pot life will be.

    The stronger the glue, the more viscous or solid the batch becomes
when equal amounts of water are added and heated up. As a matter of
fact, their test of glue strength involves only a viscosity measurement
because it is directly proportional. The number of grams required to
depress a plunger down into a quantity of glue in a measured cylinder
directly determines the percentage of heavy proteins it contains, and
these  determine the strength of the glue.

    I had to test 6 different varieties of hot hide glue before I found
one that came up to my specifications. Almost all of the commercially
available hide glue crystals are less than satisfactory to me, now that
I have found the particular batch of glue I really like. However, the
stronger the glue, the more critical it is to use. It sets faster. It
is the lightweight proteins that add the latitude which neophytes
think they need. But I'll show you another way.

    Hot hide glue can be made stronger than any other kind of wood
glue, as a rule, although many varieties are not. It chemically and
mechanically binds to wood, whereas the other glues, as a rule, are
mechanical bonds. Once it drys, it does not "creep."  So constant
pressure against a joint will not cause it to give up in time. This is
not true of carpenter glues.

    It sets by gelling, thus you get a 100% joint coverage without
voids when applied correctly. By adding salts such as urea or
"preferably" potassium chloride to the glue, you can make it do about
anything you want, and will increase its setting time, modify its
brittleness if you wish, and even make it totally waterproof if you
need it to be. Depending on the quantity of KCl you add. [KCl can be
purchased from companies who sell it to put down on icy streets,
cheap.] Other additives will cause it to bond with metals. It is a most
versatile glue, in that you are able to add water to get the
consistency you want. If you get a "cold joint" you just reheat the
joint with an iron or heat gun and keep it tight until it gells again.
You seldom require clamps with hot hide glue because of its "death
grip" it gets on the parts once it sets. After that, it draws them
together itself as it drys out.

    So by adding, first of all, more water, you get the slower setting
time again. And if you are gluing pneumatics, if you just size the
shelves first, you will improve the strength and seizing
characteristics. Just don't keep sliding the pneumatic around to
position it. Get it about right and then weight it down quickly while
the joint is warm.

    If a hot glue joint is moved while it is gelling, it becomes a cold
joint, just like solder. You aren't able to tell that the next day. It
won't break for quite a while, but then it will break, finally, usually
a few weeks later.  However, the strong hide glue has less chance of
that, and once you learn to be gentle and not disturb drying
pneumatics, you will never have an instance of that.

    The only way of making carpenter glues airtight is by filleting a
bead of it around each pneumatic. By then, you have created something
so impregnable you can never repair it again. It will have to be
remade.  It also looks sloppy.  The era of Elmers is over. It is now
the age of yellow glues which are truly and ghastly permanent.

    The only glue, other than hot hide glue that you should use for
wood bonding in players is liquid hide glue. And by sizing both pieces
first before the bond is made, it should work pretty well. You can also
make your own liquid hide glue, but that's another story.

    The important thing to remember is that there are as many
differences between hide glues as there are player pianos. They vary
widely. Each has an optimum purpose, I suppose, but give me the strong
stuff, and from there, whatever I need, I will make. Without the heavy
proteins, nothing else you do to it will improve it much.

    The present batch is 2XA hide glue, lot 9563 from Milligan and
Higgins. Now, that's some real glue.

Craig B.

craig_brougher@msn.com