The Efficacy of Animal Glue

RANT WARNING!

“Hot hide glue is all right, but it’s water soluble and won’t last.”

I have had it up to Pussy’s bow with the raft of misinformation regarding hide glue on internet fora and in newsletters etc. from people with little to no experience of it, who perpetuate myths and untruths about the stuff.

Why should you listen to yet another blogger and his rhetoric? Well of course you don’t have to; though I believe my qualification (virtual daily use of animal glue for forty years) affords me at least some credence.

Animal glue, whether asinine, bovine, caprine, equine (hence horse sauce – my preferred appellation), leporid, orcervine, ovine, piscine, porcine – bone, hide or skin, is indeed soluble in water and that is one of its greatest assets (animal glue in its dry form will keep indefinitely). Dry animal glue is first heated in sufficient water to make it brushable, however – and this is the noteworthy part – when the majority of water has evaporated from the glue (the glue is set and ‘dry’), it can, with a modicum of effort, be dehydrated/rehydrated, permitting the repair or repositioning of components.

I think when some people say “animal glue is water soluble” they mean it’s not waterproof. That is true of unmodified animal glue (it can easily be made waterproof), but its most widely used competitor, polyvinyl acetate adhesive (PVA or ‘white glue’), is not waterproof either.

As any furniture restorer can attest, veneers or furniture glued with animal glue can be disassembled quite easily with steam/hot water and mechanical assistance, but even tepid water alone takes a considerable time to soften the glue to the point that the bond is compromised.

Although animal glue was known to the ancients, virtually every piece of furniture made since the mid 1600s was stuck together with animal glue and thousands of antiques dealers and their customers around the globe are quite happy with the results thank you very much!

Humid weather will not cause a room full of antique furniture to suddenly (or slowly for that matter) slump into a pile on the floor. Even roughly constructed nineteenth-century ‘country pine’ furniture survived the hot caustic stripping tanks of the 1970s intact (all right, a few drawers might not have survived the nightmare solution, but it was never fine cabinetwork to begin with).

I began a simple experiment in April, 2012: I took a 24″ x 14″ (610mm x 355mm) piece of 5/64″ (2mm) thick mahogany veneer and glued it onto a 3/4″ (19mm) thick pine board (actually two boards rubbed together). I applied unadulterated animal glue to one half of the veneer/board and PVA to the other and then hammered the animal glue side and cramped the PVA side.

The un-sealed veneered board has been lying outdoors on top of a stack of timber for twelve months, during which time it has been baked in 42° C (108° F) sunlight, drenched with rain and crapped on – not by me I might add!

The PVA more or less gave up some months ago, but the animal glue has held up quite well – at least it has largely kept the veneer in contact with the board.

test_board_01aWeathered test board; animal glue on the left and PVA on the right.

Recently, following twelve hours of steady rain (after which I observed pooled water on the animal glue side), I checked the trial board and the exposed animal glue at the edges of the veneer was tumescent, but even pushing with some force, I couldn’t insert a pallet knife more than 3/16″ (5mm) between the veneer and the board.

And while my tongue’s warm…

Following the post, Making Rabbit Skin Glue – Easy as Piss! I received some mail on the subject (including a couple of offers of whole deer and goat skins and significant quantities of fresh, intact rabbits! Thank you, but no.).

I would like to clarify one point: Hides and skins are initially boiled to release collagen, but at no time should animal glue be boiled or the protein chains that afford the glue its strength will break down.

To prevent rapid degradation and to ensure long life, the working temperature of animal glue should never exceed 60°C (140°F).

Jack Plane

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About Jack Plane

Formerly from the UK, Jack is a retired antiques dealer and self-taught woodworker, now living in Australia.
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25 Responses to The Efficacy of Animal Glue

  1. Ian Wells says:

    Well said .

    Like

  2. Benoît Van Noten says:

    My father had bought antique furniture in the year fifties. There has been some failure but not due to humidity but on the contrary, my father attributed it to central heating and not enough humidity. What do you think of it?

    Like

    • Jack Plane says:

      There’s no doubt that centrally heated homes (and closed rooms with a sunny aspect) have contributed to some furniture becoming too dry. The solution is simple though: Keep a vase of flowers, a goldfish bowl or some other source of water in the room.

      JP

      Like

  3. Good post Jack, I just finished reading Stephen A Shepard’s book on hide glue because of all of the different opinions I have read about it. You can’t beat it’s longevity – King Tut had furniture still secured with hide glue after 3000 years plus.

    Like

  4. Patrick Endicott says:

    Thank you very informative
    I always worried about using hide glue in wet locations and usualy changed to PVA for that work but will not do this in the future
    I had always wonderd how window were glued in the past assuming that the paint protected the glue but it sound like the glue was not as affected by the weather as I thought

    Like

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  6. millcrek says:

    Jack, I posted a link to this post, I hope you don’t mind. I think more people who know what they are doing should rant more, there is way to much misinformation that is never challenged by respected voices.

    Like

  7. Brian Eve says:

    Well said. My favorite kind of rant, backed up with an example to put your money where your mouth is.

    Like

  8. Jack Plane says:

    I received an email from an established restorer in Leichhardt, NSW who included this link on the matter of animal glue versus modern adhesives.

    JP

    Like

  9. knoxonwood says:

    One of our members printed a piece in the latest Knox & District Woodworkers Club news letter about hot hide glue. I have never read such drivel in my whole life and who knew that the smell of hot hide glue made dogs ejaculate. http://www.alchester.com.au/kdwc/kdwcnews/20130401.pdf

    Like

    • Burbidge says:

      Ah, I too had seen the Strange Case of Dr Jeckyl and Mr Hyde-Glue…

      As for the dogs, maybe you have to raise the temperature up to 80 degrees for that outcome?

      Like

  10. knoxonwood says:

    He has done another really bad piece on hot hide glue, http://www.alchester.com.au/kdwc/kdwcnews/20130501.pdf which he copied from another web site, http://www.native-art-in-canada.com/rawhide-glue.html. He obviously has never made or used any glue or he wouldn’t keep telling everyone to boil the skins.

    Like

  11. Andy says:

    Thanks for the rant; I’m just starting to get going with wood working, and I’d been trying to sort through all of the claims about hide glue. Seeing someone actually take the time to test things is encouraging!

    A question: what’s your opinion on liquid hide glue, as opposed to hot hide glue? I’ll admit that I’m not quite sold on having to prep my own glue, but again, there seem to be some mixed messages coming out about the liquid kind.

    Like

    • Jack Plane says:

      I have only tried the Titebond liquid hide glue which I purchased once to effect an emergency repair on a large bookcase in a customers home. It was perfectly satisfactory.

      I regularly add urea to hot glue to extend its open time and on the occasions there are leftovers, I will add further urea to any leftovers for use at room temperature. I have the hot glue on the go virtually every day, so the reality is I seldom use the room temperature glue and usually put it back in the pot with fresh glue beads.

      The short answer to your question is that cold glue works very well, but the hot version is more versatile.

      JP

      Like

      • Andy says:

        Thanks. For the amount I use right now, and the fact that I tend to only get to work in short bursts, a glue pot isn’t really practical. But I’d like to start using hide glue, at least once my current bottle of Titebond is used up.

        So knowing that the cold stuff is at least acceptable is reassuring.

        Like

  12. John Ford says:

    Very interesting test.
    I notice that the PVA side of your test piece has more breaks/cracks than the hide glue side. Do you think that’s coincidence, or possibly cause and effect? PVA has more “creep” than hide glue, could that have anything to do with the cracking on the PVA side?

    Like

  13. I’m admittedly late to the party here, but by way of perspective: I’m a pipe organ builder. While furniture and cabinet makers talk about having air tight joinery, our trade actually requires it to be literally so and until after World War II hide glue was the only adhesive you’d ever find in an organ. I’m currently restoring an instrument built in 1908 and there’s not a failed glue joint in sight. Anybody claiming hide glue joints are not proof against changing humidity has thousands of air tight pipe organs to explain. Assuming the joints don’t get seriously wet (dripping ceiling, standing water) there simply isn’t a problem with the longevity of the adhesive. Indeed, A lot of the higher dollar organ builders still use hot hide glue for new construction.

    Like

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