Sign of Hot Hide Glue going bad?

[Craig Bumgarner]

I've noticed the last batch of hide glue I'm using is becoming less viscous as time goes on. I store freshly made HHG in the freezer and take out 2-3 ounces in chunks as needed. I keep the HHG I'm using in a squeeze bottle and heat to 140F in an electric kettle with thermostat control. I do not leave the bottle in longer than I need to for the job at hand and other wise leave the bottle setting out at room temp. I don't use a lot of HHG, so it might be 3-4 weeks before I get more from the freezer, so the glue is sitting at room temp for a month.

The bottle full I was using last month, got so it would not gel even at room temp. I threw it out. The current bottle full which is from the same batch in the freezer gels at room temp, but after recently, it too eems less viscous and does not gel until it is completely cooled off. When fresh, it seems to gel at higher temps.

Is this a sign the glue is going bad? My testing of joints I've glued with it seem to hold okay. The glue does not smell bad as I have noticed occasionally with HHG. If it is bad, any idea why? I don't think I'm over cooking it. Too long at room temp?

Thanks,

[Barry Daniels]

Too long at room temperature. It would be better to re-freeze it or at least put it in the refrigerator.

[Craig Bumgarner]

Too long at room temperature. It would be better to re-freeze it or at least put it in the refrigerator.

Okay, thanks, sounds right.

[Randy Roberts]

Craig,
Think of HHglue as Jello. Great media for bacteria and other flora and they digest it. The rate they digest it varies with temperature and number of organisms, and to a certain degree it is more exponential with temperature than linear.
Dry, the bacteria can't do anything to it without the moisture. Frozen, they can't do anything. Refrigerated they can digest it but they can't do it at a rate that matters for quite a while.

It is a protein, and so it also degrades with temperature. The higher the temperature and longer the time at higher temperature, the more of it gets broken down, and is no longer "glue".

[Todd Stock]

My hide glue info to students:

- Keep dry hide in sealed containers (a new gallon paint can will hold 5 lbs of dry hide), and stored in a cool, dry location

- Use distilled water to make up the glue; pH matters, as does other contaminates, so avoid the issue

- Good glue crystals should hydrate quickly...an hour should see the glue ready to heat. If the dry crystals seem to be taking a long time to absorb the water, the glue may have degraded in storage due to excessive heat, damp conditions, etc. Toss and store the new stuff properly.

- If the prepared and 'fridge-stored glue is moldy, toss

- If the 'fridge stored glue shows reduced tack and poor 'stringing', toss

- If reheated more than 3 times, toss...at 10% tensile & shear strength loss per reheat, the glue is only 3/4's as strong as fresh after the third reheat, while after a half dozen reheats, the glue is 1/2 as strong as freshly made

- If heated beyond 150 deg F, toss...I run the water bath at 150 deg to get 140-145 deg glue temp...but when I need greater penetration for repair work, I heat to 170, then promptly toss the leftover glue

- Use a sealed container for storage and use - an 8 ounce glass 'Mason' style jelly jar or capped 2 ounce poly squeeze bottle in combination will handle most shop jobs...put the lid on when the pot gets turned off and the Mason jar will vac seal as it cools.

- Either multiple Hold Heets with fitted poly covers to hold the jar and bottle or a modified cover for a Proctor Silex hot water pot work well in a busy shop setting. A hot pot that holds just clean water at 150 deg F for cleanup is handy. An open glue pot with all that dried, baked on glue residue looks wonderfully romantic for casual visitors, and makes the shop smell good (at least to me), but invites mold, dust, and other crud to set up housekeeping in the sticky stuff. Copper Hold Heet liners will provide some protection against bacteria, but using a separate container in a water bath avoids the issue.

- Use a clean brush that has not been sitting out collecting contaminants...a 1" artist's Taklon brush or a linden paste (which has anti-bacterial properties) will hold up to repeated clean/use/clean cycles. I run my plastic handled, stainless ferruled Taklon brushes through the dishwasher on the 'sterilize' cycle...look for brush sales online or at local crafts stores and pick up several so that they can be cycled through a good cleaning. Linden bastes may be rinsed and dried, then rinsed in hot, clean water before use.

- 192g high clarity for everything except bridges, which get fresh 315g

[Paul Breen]

- If reheated more than 3 times, toss...at 10% tensile & shear strength loss per reheat, the glue is only 3/4's as strong as fresh after the third reheat, while after a half dozen reheats, the glue is 1/2 as strong as freshly made

Todd, how do you know this? Does this come from a study or did you do you're own?

[Mario Proulx]

I have been using 192 high clarity for bridges for 17 years. Nary a problem, despite my bridges being most likely the tiniest in the steel string guitar world...

No amount of time at room temp is good. I've also given-up on freezing mixed glue. Freezer burn is real.

It's not -that- hard, nor does it take that long to make a fresh batch, especially a tiny batch if you only need a wee bit.

For refrigerated glue that you think should still be good, just make some little glue cookies(dogs love 'em, if you have one... ) on a clean workbench. If the bead of glue flattens out and the "cookie" is nearly flat, toss the glue. If it stood-up and toughened into a nice gelatin cookie(do a few with freshly mixed and heated glue to see what it should be like) then you're still good.

For bridges or joining plates, --always-- a fresh batch. Why chance it?

[Todd Stock]

M&H tech support...and 40 years of using the stuff. There is a sensible decrease in tack after each reheat if you take the time to try it. Sort of makes sense - you are cooking the glue at each reheat, and heat breaks down the tough, long chain molecules. Glue is cheap - M&H sells it for hamburger prices in larger quantities.

[Jim McConkey]

Todd, for the benefit of those who don't know, what is M&H? Always beware of using acronyms.

[Todd Stock]

Milligan & Higgins...the hide you buy from Tools for Working Wood, Highland, SM, LMII, and pretty much any other woodworking or luthiers supply is likely to be repackaged M&H. Tanex TOPAZ is the other glue that I've used - expensive delivered from the Czech Republic, but also very good stuff.

[Paul Breen]

Thanks Todd.

I have been using hot hide glue for around 15 years and was unaware of the appreciable decline you mention in tack at each re-heat. I did some digging on the internet after you posted the glue's tack degrades 10% at each re-heat. Not easy to find but I did run across two different references that supported this claim but only as a passing statement with no mention of the the 10% rate of decline, which is substantial, or any suggested rate for that matter.

I have yet to have any failures due to multiple re-heats of a glue batch, including structural repairs like bridge replacement. Ignorance is bliss, as they say. I am well set up to use hide glue and am very comfortable with it as an everyday glue for instrument repair. No excuse to not freshen things up more frequently now that I am aware of this.

[Todd Stock]

Given how the glue might be treated (cooking all day at 150 deg F versus an hour at 135 deg F), I doubt any manufacturer will commit to a written statement on reheat strength, but that's what the M&H rep gave me...betting it is a 'worst case'. I doubt the issue will show up unless used in a stressed application like a bridge. I don't worry too much on my own stuff - the joinery is tight and I know what the surfaces look like. On a repair, it can be a real challenge to get a gluing surface anywhere as clean and even as a new guitar. Hence, 315g - stronger in an imperfect world is usually not a bad thing.