Rabbit Skin Glue is a high grade glue made of pure rabbit collagen. It is a granular glue that is easy to dissolve in water for use as a size in preparing canvas and panels and in distemper painting. It easily dissolves in water. This makes it ideal for use in gesso and as a medium for distemper painting.
Stronger than most modern adhesives, rabbit skin glue is used in traditional woodworking, gilding and painting techniques. First soaked in water and then heated in a water bath, it is applied warm, and gels when left to cool. In woodworking, rabbit skin glue’s solubility in water makes it reversible, while its “open time” allows for repositioning. In painting and gilding techniques, it is used both as a size for canvas and boards, in recipes to make traditional gesso, and in distemper paints.
Animal glues vary in strength, but rabbit skin glue usually offers the highest strength, viscosity and elasticity. True rabbit skin glue tends to gel at lower temperatures, making it easier to use in gesso applications. Otherwise, glue made from bovine collagen are comparable.
Initially the hides are kept in a lime slurry pit for 1-3 months for lime curing. This process helps loosening of collagen bond in hides so that it can be extracted easily. After lime curing the hides are washed several time to remove excess lime and than the glue is extracted from by cooking in boiling water. The extracted glue is then concentrated with the help of an evaporator. The concentrated glue is dried in drum driers and pulverized for final packing.
Animal glues are adhesives that are high molecular weight polymers in organic colloid form from hydrolyzed collagen found in animal hides, connective tissues and bones. Glue contains two groups of proteins: chondrin, which accounts for its adhesive strength, and gluten, which contributes jelling strength. Animal glue is derived from the simple hydrolysis of collagen, which is the principle protein constituent of animal hide, connective tissue and bones.
Hide and bone glues make up the two major types of animal glue. Hide glue, which is by far the superior of the two, yields a fairly neutral pH in solution, usually in the range of 6.5 to 7.4, although wider variations are possible. Bone glue is generally acidic, having pH values of 5.8 to 6.3. A glue having a high acidity absorbs less water and tends to set more slowly than a glue having low acidity.
Animal glue is soluble only in water and insoluble in oils, greases, alcohols and other organic solvents. When placed in cold water, the glue absorbs water and swells to form a gel. When heated the glue dissolves to form a solution. When the solution is cooled the glue once again forms an elastic gel. This property is thermally reversible and upon application of heat the gel liquefies. The gelling or melting point of an animal glue solution can vary from below room temperature to over 48.9° C (120° F), depending upon the grade, concentration and presence of modifiers in the glue.
A side note to provide context: Animal glues have been in use since ancient times. Paintings and murals from the period between 1500-1000 BCE show details of wood gluing operations. A casket removed from the tomb of King Tut shows the use of glue in its construction. Many art objects and furnishings from the tombs of Egyptian pharaohs are bonded or laminated with some type of animal glue. The first references in literature concerning glue providing simple procedures for making and using animal glue were written about the year 200 BCE.
Much of the original development of adhesives based on natural products has come in the woodworking and paper industries. Prior to World War I, there were simply no other options. The five classes of adhesives used most were animal glues, liquid glues (lower strength variety of fish or animal glue stabilized with acid for a long term storage), casein and vegetable protein glues, starch glues, and blood albumin glues. Also used to a lesser degree in adhesive formulations at the time were sodium silicate, mucilage, asphalts, gums, shellacs, and natural rubber.
The above information was found on a suppliers site.
http://www.naturalpigments.com
Here are a few images of how the product is stored and shipped.
