There's open time available if you want it, though maybe not enough and
at the cost of convenience. The simplest way to get longer open time is
to work in a hot room with warmed wood.

Hot glue is graded by "bloom strength," how many grams weight it takes
to rupture the surface of a standard jelled solution with a standard
poking instrument. Think of sticking your finger into a bowl of jello;
this was the actual test that was quantified as gel strength. As the
bloom gets higher you have a shorter open time and more strength. Other
factors that shorten the open time are cold wood (Victorian woodworkers,
IIRC, would build up fires of shavings to warm the joints before glue-
up), cold room, glue under 150 F., glue too liquid (so less volume on
the joint to hold the heat). There are others too. It gets complex: for
instance, if you leave glue in the pot and re-warm it, it will break
down a bit, and you find that you are working with a glue that has, in
effect, a lower gel strength than what you started with. It doesn't take
much to chill hot glue; I found that even in the Bay Area, where a
chilly day is in the forties, I couldn't use hot glue for bookbinding
when my house was unheated in winter. Or you can get longer open time by
adding a small amount of a "gel suppressant" like urea to the glue,
which will extend the open time; commercial liquid hide glues stay
liquid by adding lots of gel suppressant, but you needn't be extreme.
"Old Brown Glue" adds some urea, but it isn't really a liquid hide glue;
it is solid at room temperature and requires some heating.

Tools for Working Wood offers 1-pound quantities of hot glue in 192
grams, 251 grams, and 315 grams bloom strength:

http://www.toolsforworkingwood.com/Merchant/merchant.mvc?Screen=PROD&St-
ore_Code=toolshop&Product_Code=MS-HIDEGL.XX&Category_Code=TI

http://tinyurl.com/26g7w4p

 They say that 192 would be traditional for veneering, 251 for cabinet-
 making, 315 for high-stress areas like instrument necks. Makes sense to
 me as a useful range for woodworking, going from what I know from
 bookbinding. I would guess that a violinmaker might use glue even
 lower, since he wants the body joints to break before the wood does;
 somewhere I got the impression that this might be down around 150
 bloom, but you can buy glue down to at least 130 or so, and up into the
 500 or 600 range (but there is a price break over 391 gram, which is
 what I use for binding based on research published by the Government
 Printing Office back in the 1920s or 1930s). You can get a wider range
 of grades, by steps of maybe 20 grams from the low 100s to the 600s
 (IIRC) from Bjorn Industries, but you have to buy 5 pounds minimum
 (that's enough to last me for several years):

http://www.bjorn.net/index.html

 Bjorn says their glue is American-made, so they must be buying from
 Milligan and Higgins, the last company making hot glue in the United
 States, but M & H's minimum order is, I believe, 50 pounds. And dry hot
 glue does have a shelf life, though it is years or possibly decades.
 Fifty pounds isn't an option for me.

Old Brown Glue says their glue starts as 192 bloom from M & H. This is
apparently on the low end for general woodworking. However, the
manufacturing process is to heat it continuously for four days mixed
with the urea:

http://www.oldbrownglue.com/articles.html

The heating would cause considerable degradation and give a glue of much
less than 192-gram gel strength if it did gel under test conditions and
could be tested. (My late teacher Theo Kahle used a similar process for
making cold glue for repairing parchment manuscripts, though he would
start with very high-bloom gelatine and rewarm it for half an hour or so
every day over a period of months.) So to get the extra-long working
time of OBG, you have the trade-off of having an extra-weak glue. This
makes good sense for Patrick Edwards, who is a furniture restorer and a
specialist in marquetery; in conserving cultural artifacts of high value
you can assume that they will be treated with some care, and if they do
break, you want your joint to fail, not the wood. But that doesn't make
it a good choice for, say, gluing up a new chair for active use; this
would make strength more important, and suggest a higher gram strength.

Personally I would avoid OBG because of the urea. Sources on modified
hot glues say that a gel suppressant is only active in the liquid stage,
when it is supressing the gelling, and that it becomes inert when the
glue is dry. However, in my field in the nineteen fifties, urea had a
brief fashion as a treatment for restoring flexibility to unusably
brittle vellum manuscripts; it worked in the short run, I think by
holding a higher moisture content in the vellum, but in the long run it
proved disastrous, causing the manuscripts (IIRC) to become irreversibly
sticky and also encouraging mold. Perhaps it is prejudice on my part to
extend the bad results in treating vellum to the very different
situation for hot glue; but why take risks? The urea isn't
indispensible.

Tom Conroy Berkeley


Cliff Rohrabacher wrote (snipped and paragraphs compressed):

"I'm surprised when people express doubts about the relative strength of
hide glue.The stuff is plenty strong. If the test is that it has to be
stronger than the wood it's gluing then it passes the test gloriously...

"The reason I=A0 tend not to=A0 use it, is the simplest of them all :
Ease of use. When you have a complicated assembly, you need open time.
Hide glue presents one more challenge to manage because you don't get
very long at all..."
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