Soapstone hot hide glue pot- the only one?

Construction and repair of Classical Guitar and related instruments
SteveL123
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Joined: Thu Feb 09, 2017 5:05 pm

Soapstone hot hide glue pot- the only one?

Post by SteveL123 » Thu Jan 11, 2018 3:24 am

I just made an electrically heated Soapstone bridge removal iron. Since I don't have a hot glue pot and don't plan on buying one, the thought occurred to me to make an add on soapstone hot glue pot. It holds approx 1 oz and because of the mass of the soapstone pot, keeps the glue temp very stable.

The hide glue granules I have is around 25 years old. I wonder if it is still good? After it is mixed with water and heated up to 140F, it is not clear but rather murky. Is that good or bad? What is a good test for the hide glue?

Edit: I searched online for "soapstone hot hide glue pot" and surprisingly came up empty. Hide glue was invented way before the iron age and you'd expect the first hot glue pots were made from soapstone. Soapstone bowls were the first cooking vessel made by man and it stands to reason that it was also used for making hide glue. Am I the only one with a soapstone glue pot?


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Last edited by SteveL123 on Fri Jan 12, 2018 2:41 pm, edited 1 time in total.

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Michael.N.
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Re: Soapstone hot hide glue pot

Post by Michael.N. » Thu Jan 11, 2018 9:05 am

I've had glue that's 50 years old. still worked perfectly well. Probably just as good as the day it was made. Murky is probably fine too, a lot of it is like that.
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SteveL123
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Re: Soapstone hot hide glue pot

Post by SteveL123 » Thu Jan 11, 2018 2:38 pm

Michael.N. Do you know what makes some hide glue clear and some murky? When clamping a rosewood bridge with hot hide glue, how much clamping pressure should be used? I have read it is a chemical bond, not a mechanical bond so scratching the surface actually hurts the bond strength. Do you want to squeeze as much of the hot hide glue out as possible?

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Michael.N.
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Re: Soapstone hot hide glue pot

Post by Michael.N. » Thu Jan 11, 2018 3:41 pm

You need very little clamping pressure. I glue bridges on (not large modern guitars) using finger pressure alone and it's not as though I'm pressing down hard. You can also do a rubbed joint too. The secret is to get the glue consistency right (for critical joints) and mate the pieces before the glue gels.
I don't know what makes some glue murky. Presumably it's something that is held in suspension. It's never worried me in the slightest because murky glue has virtually always performed to my expectations. Bone glue is often murky and I've never had problems with that. You can test by gluing a series of offcuts together. I usually do a mix of different woods and even end grain to side grain (size the end grain well first). You can also do the tack test between the index finger and thumb, pulling them apart over a period of a minute or two. After a while the glue should start to feel very tacky. It's easier to see someone do it than explain it. Whenever I get a new batch of glue it goes through the tests. You only need to do the tests once and that batch is good, assuming it's performed well. In the last 15 years or so I've only had one batch which gave me doubts. That was murky too but it also felt rather greasy. It didn't seem to perform all that well in my tests. I sent the stuff back.
if you are really worried about murky glue drop Eugene Thordahl an email at Bjorn industries. He's a hide glue specialist and a trained chemist. If he doesn't know no one will. He's always been quite happy to answer a few questions I've had over animal type glues and their properties.
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Douglass Scott
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Re: Soapstone hot hide glue pot

Post by Douglass Scott » Thu Jan 11, 2018 5:04 pm

SteveL123 wrote:
Thu Jan 11, 2018 2:38 pm
Michael.N. Do you know what makes some hide glue clear and some murky? When clamping a rosewood bridge with hot hide glue, how much clamping pressure should be used? I have read it is a chemical bond, not a mechanical bond so scratching the surface actually hurts the bond strength. Do you want to squeeze as much of the hot hide glue out as possible?
I buy most of my hide glue from Bjorn Ind., the company Michael mentioned above. They sell a high clarity grade, but regular hide glue is a little murky. Maybe your old glue was always that way.

SteveL123
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Re: Soapstone hot hide glue pot

Post by SteveL123 » Thu Jan 11, 2018 11:02 pm

Michael.N. wrote:
Thu Jan 11, 2018 9:05 am
I've had glue that's 50 years old. still worked perfectly well. Probably just as good as the day it was made. Murky is probably fine too, a lot of it is like that.
Amazing! Funny that I have a small plastic bottle of unopened FG xx glue (forget the number) bought from LMI at the same time as the hide glue and it is super thick and stringy and smells sour, totally useless. So thick it can't be squeezed out of the bottle nor could I use a stick to get it out.

SteveL123
Posts: 548
Joined: Thu Feb 09, 2017 5:05 pm

Re: Soapstone hot hide glue pot

Post by SteveL123 » Thu Jan 11, 2018 11:04 pm

Douglass Scott wrote:
Thu Jan 11, 2018 5:04 pm
SteveL123 wrote:
Thu Jan 11, 2018 2:38 pm
Michael.N. Do you know what makes some hide glue clear and some murky? When clamping a rosewood bridge with hot hide glue, how much clamping pressure should be used? I have read it is a chemical bond, not a mechanical bond so scratching the surface actually hurts the bond strength. Do you want to squeeze as much of the hot hide glue out as possible?
I buy most of my hide glue from Bjorn Ind., the company Michael mentioned above. They sell a high clarity grade, but regular hide glue is a little murky. Maybe your old glue was always that way.
Yes, maybe so. I will do the glue tests that MichaelN suggests.

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