“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 alcohol or 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.
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).