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PostPosted: Mon Feb 03, 2020 2:54 pm 
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Joined: Sun Mar 09, 2014 8:13 pm
Posts: 2163
I've done a preliminary and unscientific experiment, involving the addition of salt to hot hide glue, to increase working time. The result is encouraging. As a biochemist, I can design a better experiment with more controls, but as you can see, the addition of salt seems to work.

I used 1/2 cup of prepared 251 gram strength hide glue, in a 1:1 ground glue to water ratio. I heated the glue to 148° F.

Initially, I placed 1 drop of the glue between my clean index finger and thumb, opening and closing my fingers, feeling for tack while keeping time. I know this is subjective and my body temperature affects timing.

There was good tack at 36 seconds. It ended at 51 seconds. I repeated this 2x, with only a variation of 2 seconds. I also glued a piece of spruce to another piece of spruce at 50 seconds, which held. I tried it at 1 minute 5 seconds and it didn't. So, I think we can safely say that the working time for unadulterated hide glue is no longer than 1 minute.

I added 1/16 of a teaspoon of plain, non iodonized table salt to the pot and allowed it to stay at 148°F for 5 minutes, after mixing.

I repeated the experiment. This time, 1 drop of hide glue became tacky between my fingers at 1 minute 57 seconds.

The tack ended at 2 minutes 35 seconds.

I then placed the hot glue on a piece of Honduran mahogany. I clamped it to a piece of spruce after 2 minutes 35 seconds. 30 minutes later, the joint was holding without clamping, although not under stress.

I think it's safe to say that the addition of a small amount of salt increased the open time of hot hide glue by a factor of 2x, conservatively. I need to get equipment to measure the affect on the strength of the bond.

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PostPosted: Mon Feb 10, 2020 4:04 pm 
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Joined: Wed Nov 02, 2011 9:13 pm
Posts: 191
It would be interesting to see how the glue holds up down the road.

I'm also wondering now what sort of effect local waters have on hide glue ... does hard water react differently from soft water? Did Stradivari's glue have some property from Cremona water that other places didn't have?


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PostPosted: Mon Feb 10, 2020 6:56 pm 
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Joined: Fri Mar 03, 2006 7:09 pm
Posts: 6092
Location: Hegins, Pa
that is a good question
Not sure what RH or hardness effect would have

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Blues Creek Guitars Inc
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PostPosted: Mon Feb 10, 2020 10:52 pm 
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Joined: Sun Mar 09, 2014 8:13 pm
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I'm hoping to have at least a partial answer to this question soon.


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