This is the first part in what will hopefully be a two or three, or even four, part series on Hide Glue. Very few people are making really high quality glue these days. The plan is to provide a solid introduction with practical steps to making high quality glue, and to cover the basics of using it. Following posts will have to wait for time, energy and pictures. You can subscribe on the right to receive notification of new posts via email so you don't have to stay glued to your screen.
Collagen Glue, aka hide glue or animal glue, is made from the parts of animal bodies which contain large amounts of collagen. Collagen is abundant in animal bodies, but certain parts are highly concentrated sources of relatively pure collagen of the type useful for making glue. Commonly used glue materials are skin (including fish skins), sinews (the fibers which connect bones to muscles) and antler. Fish air bladders have been used to make an especially strong glue. The common practice of using skin scraps to make glue has given us the term Hide Glue, which is generally used for all collagen glues regardless of the raw material used to produce it. The materials are cooked long and slow to dissolve the collagen, followed by drying the resulting gelatin which is then reconstituted in water as needed.
There is a misunderstanding that glue is made from hooves. The horny outer covering of hooves does not contain useful collagen. Hoof sheaths and horns are more physiologically related to hair and are primarily composed of keratin which does not go into solution when cooked in water. The bones and ligaments inside the hoof do contain a lot of collagen and have commonly been used to by glue boilers to make glue and neatsfoot oil. Making glue from the whole lower legs is not generally a good choice for home producers due to contamination from fats and other unwanted substances. If you try to make glue from the hoof sheath itself, it won't work. I know, I’ve tried. Instead, I recommend extracting some of the glue making parts from the lower legs and feet and then using just those, but that is for another post.
The gelatin used in cooking (jello, etc...) is just a refined grade of collagen glue. Meat stocks that gel on cooling, also do so as a result of dissolved collagen. Gelatin is a very nourishing food.
Hide glue has many traditional uses. It is a very strong glue when well made and properly used. Hide glue always remains water soluble, meaning that the joint will come apart if the glue reaches a certain moisture content. As one can imagine, the water solubility of hide glue is often inconvenient and is one of the major factors in it’s replacement by modern moisture resistant glues. Although sometimes inconvenient, hide glue’s water solubility can be an advantage. It is still used in making fine musical instruments and by a few forward looking fine furniture makers, because the item can be completely disassembled with the application of steam to the joints. Easy disassembly allows for repair without incurring any damage to the wooden parts. Imagine the crime of repairing some amazing 300 year old violin using a permanent glue. It would be severely damaged a hundred years from now when it requires repair again.
Aside from water solubility, another factor in the replacement of hide glue by modern glues is the inconvenient fact that it must be used while hot. Glueing up projects may be stressful even with modern glues, requiring speed and accuracy, but working with hide glue is much more exacting. The glue should remain liquid until the joint is set and clamped, which means that it must remain warm. Unfortunately, it is not advisable to apply hide glue to hot wood in order to keep the glue warm, because it can cause the wood to absorb all the glue.
The final blow to hide glue in modern industry and arts is that it does not store well in it’s wet state. The old glue must be thrown out frequently and a new batch prepared. Rotting glue loses it’s strength rapidly. Attempts to make preserved hide glues that could be stored in a ready to use state have been made, but results have never been quite up to the traditional product. So, real hide glue is just not convenient.
One other place where hide glue has retained some use is in the arts for sizing and gilding with gold leaf.
In paleotechnology, hide glue has many uses and is the strongest glue that we can make. It is used to hold sinew wrappings in place, to size over paintings, as a binder for paint pigments, to glue materials together, and to glue the sinew backings or other coverings onto bows. Making fine quality hide glue is well within the means of homescale technologists like you!
Making: Hide glue is produced from Collagen sources in animal bodies such as skin, sinew and antler. Accomplished by dissolution into hot water by long cooking, followed by drying the resulting gelatin and then reconstitution in water.
Advantages of hide glue: accessible (you can make it!), easy to make, strong, easy repairs, nontoxic.
Disadvantages of hide glue: must be used rapidly before it cools and jells, joints come apart when moist, glue rots easily once made.