Animal glue
[1] These protein colloid glues are formed through hydrolysis of the collagen from skins, bones, tendons, and other tissues, similar to gelatin.
Glue deriving from horse tooth can be dated back nearly 6000 years, but no written records from these times can prove that they were fully or extensively used.
Between 1500 and 1000 BC, it was used for wood furnishings and mural paintings, found even on the caskets of Egyptian pharaohs.
[6] Evidence is in the form of stone carvings depicting glue preparation and use, primarily used for the pharaoh's tomb furniture.
[7] Egyptian records tell that animal glue would be made by melting it over a fire and then applied with a brush.
[8] Ancient Greeks and Romans later used animal and fish glue to develop veneering and marquetry, the bonding of thin sections or layers of wood.
[6] Animal glue, known as taurokolla (ταυρόκολλα) in Greek and gluten taurinum in Latin, were made from the skins of bulls in antiquity.
[9] Broken pottery might also be repaired with the use of animal glues, filling the cracks to hide imperfections.
[6] During the medieval ages, fish glue remained a source for painting and illuminating manuscripts.
[7] Native Americans used hoof glue primarily as a binder and as a water-resistant coating by boiling it down from leftover animal parts and applying it to exposed surfaces.
The Assiniboine preferred longer hair, so they would plaster the strands with a mixture of red earth and hoof glue.
Davis company thrived producing animal glue during the Great Depression after shifting its focus from stenciling, selling to local box makers and other users.
Today, animal glues are sparsely industrialized, but still used for making and restoring violin family instruments, paintings, illuminated parchment manuscripts, and other artifacts.
Other aspects, such as difficulty of storage in a wet state, requirement for fresh raw materials (the animal skin cannot be rotten or grease-burned), make this product more difficult to obtain and use.
[20] Animal glues will also darken with age and shrink as they dry, giving them the potential to harm wood, paper, or works of art.
Recently, animal glue has been replaced by other adhesives and plastics, but remains popular for restoration.
Today it is used primarily in specialty applications, such as lutherie, pipe organ building, piano repairs, and antique restoration.
It may be supplied as granules, flakes, or flat sheets, which have an indefinite shelf life if kept dry.
At room temperature, prepared hide glue has the consistency of stiff gelatin, which is in fact a similar composition.
Hide glue has some gap filling properties,[24] although modern gap-filling adhesives, such as epoxy resin, are better in this regard.
[26] The significant disadvantages of hide glue – its thermal limitations, short open time, and vulnerability to micro-organisms – are offset by several advantages.
In contrast, cleaving a joint glued with PVA will usually damage the surrounding material, creating an irregular break that is more difficult to repair.
Violin makers may glue the center seams of top and back plates together using a rubbed joint rather than using clamps.
For example, a cello maker may not be able to glue and clamp a top to the instrument's ribs in the short one-minute open time available.
PVA glues create plastic joints, which will creep over time if heavy loads are applied to them.
