Hello All,
A few questions about animal glues. My understanding is that unless specified as genuine rabbit skin, most animal glues are a mix of animal sources (mostly cow, some pig) and the term “rabbit skin”, rather than denoting origin, indicates a quality of glue: high bloom strength and 100% collagen. My idea of high bloom strength is 450 or so – but I see companies selling so-called “rabbit skin” glues with lower, 350 bloom strengths. So…
1. Are there industry standards outlining what qualifies as a high enough bloom strength to denote a glue as so-called “rabbit skin”?
2. If not, what is generally accepted as a high bloom strength?
3. If a glue isn’t 100% collagen, what else is it (aside from collagen)?
Thanks if you can offer any insight on these questions!
Koo Schadler
I will let others comment on much of your question, but I would first say that there is really no governing body to regulate what a supplier calls their art materials in any enforceable way. Even ASTM is a voluntary system. If there was enforcement of a rational standard or nomenclature, we would not call something gesso when it is composed of an acrylic dispersion bulked with titanium dioxide and a filler, likely calcium carbonate. People know the term rabbit skin glue and therefore suppliers call their animal glue that term. I am guessing that most RSG sold is likely bovine.
An interesting fact is that the term rabbit skin glue is not found in any manual before the 19th century even though everyone is somehow convinced that it is the best animal glue for art making.
Finally, animal glue is not exactly collagen, it is the product created when sources of collagen are heated and extracted. The product is a mixture of amino acids. The length and degree of heating (or other chemical processes) will affect the degree of hydrolyzation.
Thanks, Brian – that’s helpful, and fascinating to hear RSG wasn’t mentioned until 19th c.! The 19th century’s reinterpreting of old master materials and methods made up all sorts of things…
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