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Hide Glue Basics


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There's plenty of info on the net regarding hide glue, however I have a few questions I'd be interested in people's opinions on. 

- My understanding is that you soak glue in cold water for half an hour or so until water is absorbed...

- Do you then bring the glue to temp 140F quickly or slowly? does it make a difference? 

- do you use as soon as it is up to temp? or is it best to let it sit at that temp for a while? 

- can you leave it too long at correct temp while doing other jobs? 

- how much do you monitor for over/under fluctuations in temp?

- Is there a point where you would consider the glue ruined if it accidentally went over XXX degrees?




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If you are referring to the crushed hide, I'd be tempted to let it soak for an hour. That way you have a much better chance of having the whole stuff fully dissolved when it's up to temperature. Heat it up too soon and you tend to get bits of undissolved glue. Of course eventually they will dissolve too.

I doubt if it makes the slightest difference how fast it is heated.

Once it's up to temperature and providing it's all dissolved it's ready to use.

You can leave it too long. There's a trade off between time, temperature and strength of the glue. The longer it's heated the weaker it becomes. The higher the temperature the quicker it loses strength. Having said that I've had glue heated at 140F for virtually all day and used it. I might not use it for critical joints but it's been perfectly fine for other things. You can also heat the glue much higher than 140F if you want a slightly longer open time, you just can't heat it at the much higher temperature for very long, maybe 5 minutes or so. After that it will start to quickly lose strength.

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This gets ritualized and made technical in so many ways.  


But using hide glue is also a very ancient practice.  The basics don't have to be complicated.  Even making it from scratch doesn't have to be complicated.  The basic idea is to take scraps of parchment skin, or animal hide, or bone and boil it down.   Then boil and reduce until you have a gel.  Then allow to dry.   There's no need to make it more complicated than that, though plenty of people do.


Using it is similar.  Rehydrate your dried gel with water and heat.   Don't let it rot from bacteria or mold.   Don't denature the protein with excessive temperature.  Soaking the glue ahead of time is usually easiest, but not strictly essential.   


What is excessive temperature? Hotter than boiling water.  So steam for example.   Traditionally this is controlled not by thermometer but by heating with simmering to boiling water in a water bath.    Again, it doesn't have to be complicated.  Though many people think it must be.


You don't have to use some fancy official double boiler either.  The basics are to put your glue in an inner pan.  Heat the inner pan by placing it in hot water.  Don't place it above the water and heat with steam, that can get too hot.   Place your glue pan in the water and you're fine.   A hard boil won't ruin anything, but is a bit hotter than is ideal.   The best is a soft boil or just on the verge of boiling.


People can also trip on the ratio of water to glue.   Since you're using the glue hot, the water is constantly evaporating out and the ratio is never stable.  Different ratios of water give the glue different consistencies, and different uses.  So just get familiar with them. 


Rub some glue between your fingers and feel how watery or thick it feels, and how fast it begins to stick your fingers together. Any lumpiness means the glue isn't dissolved yet.  Use heavier thick glue for very solid permanent joins.    Use thinner glue to work into cracks, or for joins someone might want to undo in the future.   Also, hide glue is used to make 'sizing' which is almost all water with just a little glue.  Sizing should feel like water in your fingers at first, but then begins to lightly stick your fingers together after a few seconds.   Add water if you want thinner glue.  Let evaporate down or add glue or start over if you want thicker.


Don't let your boiling water run dry.  Don't let the glue itself run dry.   Use and reuse as much and long as you want.   If you think the glue is spoiled with contamination, start fresh.  If it got too hot or you just don't like something about your glue batch, start fresh.


So make it complicated if you like.  But remember that centuries of craftsman used hide glue in a very simple straightforward way.   Fire up your double boiler.  Heat and add water until you have the consistency you desire.      





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I often add glue crystals directly into the hot glue pot; it takes about a half hour and the occasional stirring to completely dissolve it.


My glue temperature is closely regulated to 145F because numerous sources indicate the glue proteins start to break down creating a weak glue if this is exceeded for any extended length of time.

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Attached is a link to a one page report produced by the Forest Products Laboratory (U.S. Forest Service/USDA) in 1920 entitled Overheating Reduces Strength of Animal Glue which answers some of your questions, and validating this age-old observation: http://fs.fed.us/research/search/?q=9628overheating+reduces+strength+of+animal+glue%29&source=FPL&contenttype=&type


Hope this helps.



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I have the standard hide glue pot in which I put a bath of water and insert into that a jelly jar with the amount of hide glue and water I need to heat up.  Takes about an hour to melt.  I'll stir with a wooden stick to check the consistency.  Add a little more water or glue depending upon how thick I need it.  Having the water is nice as it is available for clean up of squeeze out or drips.  When done I seal up the remainder in a jar for later use and put it in the fridge.  The glue pot always stays clean that way and its easier to heat up small amounts for you current needs,



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Sometimes when I want to do a small repair, and don't want to bother mixing up a big batch of true hide glue, I use Knox Unflavored gelatin. It is indeed true hide glue made from similar animal products, but is a bit stronger in result (about 325 strength), requiring faster working times. Comes in 4 little envelopes per box. Mix one envelop with 2 tablespoons of cold water until you get a smooth mix, and then heat to about 145F. You can get this stuff at Safeway or any big grocer.

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Some take it as common knowledge that you don't do certain jobs on the first heating, and you have to heat and reheat several times for some jobs (necks, center joints, bass bars, for example), and others don't matter as much (purfling or crack repairs for example, might as well use glue from the seventh heating).  I find that all very interesting.  I suggested that on here before though, and found that it is not only NOT common knowledge, but that some think that is complete rubbish.  You decide.  Maybe that is helpful information.

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  • 3 years later...
On 10/3/2016 at 7:07 PM, Polk said:

Sometimes when I want to do a small repair, and don't want to bother mixing up a big batch of true hide glue, I use Knox Unflavored gelatin. It is indeed true hide glue made from similar animal products, but is a bit stronger in result (about 325 strength), requiring faster working times. Comes in 4 little envelopes per box. Mix one envelop with 2 tablespoons of cold water until you get a smooth mix, and then heat to about 145F. You can get this stuff at Safeway or any big grocer.

This is all new to me and I have reading about hide glue. To find out that Knox gelatin is the same and a “bit” stronger is pretty amazing. Buying a guitar with a crack in the neck. The guy tells me it has no affect on sound and from photo it looks like a very tight crack. When I see it I’ll be able to tell if I can get glue into the crack.

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1. Soaking time depends on the grain size. I usually soak the glue in the evening for the next day. 

2. I make rather small amounts. 

3. Water glue ratio depends on the purpose of the glue. I have usually one standard glue and one sticky glue. (Less water)

4. I warm it up in a special pot for warming Japanese sake where temperature can be adjusted between 40C and 70C. Rather low temperatures keep the glue longer usable. If it is still liquid  after cooling down it is not good any more (obviously!) and if mould is growing on the surface. 

5. I was once in a rush and glue was not ready. I put it in the microwave for 10 seconds. This worked ok, so the speed of warming up probably is not really important. But I guess repeated micro wave heating is not good. 

6. As long as you have a tight lid on the glue so that it can't form a skin while warm, you can keep it for a whole working day ready to use in the water bath (I sometimes forget to fill up the evaporated water in the pot) but must be rather low temperatures. Before I used a normal pot on an electric heater and glue went bad after 2 or 3 days.

7. Monitoring the temperature sounds to me like overkill. Go with the temperature as low as possible to keep it liquid and everything is fine. I can't say anything about maximum temperature because I never monitored mine. 

8. Glue in general is not very expensive (except some fish glue types). Changeing glue on a regular basis is a practical solution for having always fresh and strong glue at hand. I write the date on the lid and glue older than 1 week goes in the garbage. In summer often faster. 

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  • 2 years later...
3 hours ago, David Stiles said:

I have a niggling suspicion that my last centre seam I absent mindedly glued with 3:1 glue.   I am about to start hollowing. I suppose time will tell.   I really can't be sure but confessing it makes me feel better. 

If your joint is well done, I think there will be no problems with 1: 3 glue/water ratio. I use 1: 4 and have never had any problems, but you have to consider that the ratio is related to the gram strength and my glue should be higher than 300, I suspect close to 350 (I don't know for sure this number).

This is why, to sleep peacefully, it is a good habit to do some tests at different ratios with the glue you have. ;)

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