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So I wanted to write up a short article here to do a comparison of hide glues; hide glue it made from collagen, an animal product from bones tendons, and skin (eww). One issue with using hide glue though is that it is finicky to use – it needs a constant temperature when made from scratch using dry flakes or granules, and it has a very short open time. Liquid hide glues offer a nice solution to this problem when you want a longer open time – or so it would seem.
Unfortunately liquid hide glues have a terrible reputation in the field of lutherie. On the internet, most searches show that these glues are notorious for causing failed joints – so I wanted to do a quick and objective review of hide glues to try and get past the stigma against liquid hide glues and get to the fact behind the products. People can say what they want about the glue but without some scientific testing behind it, all of the internet comments about liquid hide glue mean nothing. So let’s get to it then.
There are two major brands of hide glue – Titebond, and ‘Old Brown Glue.’ One of the first things to notice here is that Titebond glues do not list a Bloom Strength rating online (bloom strength being the rating of strength used for measuring the joint strength created by glues). According to Luthier Robert O’Brien, a typical hide glue acceptable for lutherie has a Bloom Strength rating of 192 g or higher (Reference); Old Brown Glue has a 192 g Bloom Strength rating, and it is essentially just regular hide glue with Urea added as a preservative (Reference).
The addition of Urea weakens the hide glue, but not by a whole lot. Titebond, in comparison, contains ammonium thiocyanate (8.3%) and dicyandiamide (3.7%); it also included is polyalkene glycol (Reference). Ultimately, when it comes to hide glue, fewer ingredients and preservatives is better. Beyond the ingredients though, let’s get on to the hard evidence on glue strength.
Firstly, all of the failed glue joint comments I found on the internet were directed at Titebond’s hide glue. However, beyond this anecdotal evidence, there have been a few comparisons done on these two glues. The first is a more scientific investigation conducted by Susan L. Buck at the University of Delaware. The results of this investigation found that Franklin Titebond Liquid Hide Glue performed very similarly to regular Hot Hide Glue, but began to fail at higher temperatures and relative humidities in comparison to the Hot Hide Glue; at 84% Relative humidity and 150 Degrees Fahrenheit (two separate tests, not simultaneously), the Franklin Titebond glue failed to compare well to Hot Hide Glue (Reference). This is consistent with what others have reported on the internet in forums, etc. – glue joints made on instruments with Titebond Liquid Hide Glue begin to fail when the temperature or humidity increases, with reports my some people suggesting that the change in humidity and temperature (either while gluing up or after the joitn has dried) that accompanies the switch from winter to summer is enough to cause a Titebond Liquid Hide Glue joint to fail.
In another (slightly less academic) comparison that looked at completed glue joints, a properly cured/dried joint made using Titebond’s glue failed to separate as easily as Old Brown Glue given heat and moisture – separation of finished joints with heat being one of the key desirable features for lutherie for easy removal of necks etc. for repairs (Reference). According to the same reference, Titebond did not release without breaking wood fibers, and it took more time to release under the same conditions. Additionally, Old Brown Glue also had a higher initial tack than Titebond Liquid Hide Glue.
Fine Woodworking also did a comparison of many different types of glues; while they did not examine Titebond Liquid Hide Glue, they did look at Old Brown Glue. For tight, snug, and loose joints, Old Brown Glue performed almost identically to regular Hot Hide Glue in terms of joint strength (often outperforming the joint strength in Lbs/Square Inch) – it also even provided a significantly stronger glue joint on Ipé than regular Hot Hide Glue (Reference).
While this was of course simply a short compilation of basic evidence on the subject, there appears to be more of a stigma toward liquid hide glue than necessary given some of the evidence – however, this would appear to be largely because of the reputation of Titebond liquid hide glue. Old Brown Glue, in contrast, appears to have none (or at least fewer) of the negative aspects associated with the Titebond glue, and even outperformed Hot Hide Glue in some respects upon testing by Fine Woodworking. Given the characteristics of releasing with heat and joint strength, it would seem that Old Brown Glue behaves much more like regular Hot Hide Glue than Titebond’s Liquid Hide Glue (likely in part due to the additives used by Franklin Titebond in the production of their Liquid Hide Glue)
Now, I’m not suggesting that you immediately go out and use Old Brown Glue on your instruments. Given the reservations expressed online, I would suggest you make that decision for yourself based on the evidence – but more importantly, test out Old Brown Glue and see for yourself if you think it serves as a suitable substitute for Hot Hide Glue. Don’t judge a book by its cover: Just because Deft makes soft Nitro Lacquer doens’t mean all Nitro lacquers are soft; likewise, just because Titebond Liquid Hide Glue doesn’t always seem to work particularly well doesn’t mean other Liquid Hide Glues are all the same.
That’s all I have to say on Hide Glues for now – happy building!
As one final note on hide glues, however, an important thing to observe is that Liquid Hide Glues all have expiration dates (unlike Hot Hide Glue, which can be stored in granular form indefinitely). If you plan to test this out for yourself, always check the best before date on your Liquid Hide Glue before gluing.