Hide glue is one of the oldest and most traditional glues of all. It is made from animals, by prolonged boiling of an animals connective tissue. The most common animal that was used is the horse, but rabbits and fish can be used.
Hide glue may be supplied as granules, flakes, or flat sheets, which have an indefinite shelf life if kept dry. The glue is created when it is dissolved in water and heated, so it must be hot when used. In its liquid form it has a shorter shelf life, as the glue can start to spoil. To preserve liquid hide glue, it is ideal to keep it in the freezer till the next use.
This type of glue has a very short open time, about a minute. So it is ideal to heat the pieces you are working on or work in a very warm room. So products of hide glue will contain urea, which will increase the amount of open time you have at room temperature.
Hide glue is sold in different gram strengths, the higher the number the tackier and stronger the glue will be. For the stronger glue, you usually have to trade for a shorter open time.
The advantages of hide glue are:
- The glue is easily reversible. Glued joints can be disassembled without damage to the base wood and glue residue can be completely removed from wood pores.
- Old hide glue can be easily repaired with new hide glue. This is very important when it comes to restoration work.
- Short open time. This one works for both a negative and positive. Projects can be assembled fairly quickly because of short open time.
- Easy to clean off the exterior of joints. Even when hide glue has fully cured it can still be rubbed off with a wet rag. This will insure the exterior pores around joints will be able to accept stain evenly, where as modern glues will completely fill those pores.
The disadvantages of hide glue is:
- Its thermal limitations. Does not react well to heat.
- Short open time. Assembly must happen fast.
- Vulnerability to micro-organisms. The micro-organisms can slowly break down the glue over time, weakening the joint.