HOW TO MAKE ANIMAL GLUES
The very highest strength animal glues are easy to make on your stove at home.
Animal glue is made from the fibrous chains of proteins in animal connective tissue. Heating such tissue in water dislodges these chains, suspending them in a water solution – animal glue. If temperatures are too high for too long the chains become too short, and the glue too weak. Temperatures should be kept below 180 degrees.
The less glue is "cooked," at any temperature, the stronger it will be. To reduce cooking time the tissue can be plumped up by soaking for a couple of days. It can be plumped even further by adding a small amount of lye, exposing the protein chains to easier assault by water. One side benefit of plumping with lye is that oil and grease become soap, easily flushed from the stock. The lye must be washed clear before cooking begins. Generally a mild acid, such as vinegar, is used to neutralize any residual lye. Stock prepared in this way needs far less cooking, yielding stronger glue. But not all that much stronger.
Glue made quickly, from unplumped stock, is only slightly weaker, but much easier to make.
SINEW GLUE – Make from leg or backstrap sinews, or from sinew scraps. Put sinew stock in a large pot and cover with water. Simmer at 170 degrees for about 24 hours or more, stirring occasionally. Toward the end remove the lid and let the mix evaporate down to a very light syrup – just barely thicker than water. During the last hour of simmering occasionally scoop off fat, foam, and impurities. Bring the mix to a light rolling boil for the last ten minutes or so. This will not degrade the glue, but will roll all impurities up to the surface where they can be scooped off.
While removing this chaff, keep the temperature high enough to prevent skin from forming on the surface – the very strongest part of the glue skins off first. No need throw out the debris along with the worst.
The longer the glue is simmered, the weaker it becomes. The first pouring makes the best glue with the best and weakest at the bottom. The Turks used to gather ten hours or so of highly strained horn-sinew flight bows. You may want to make the first pouring for maximum strength glue. Stronger glues can be used on first pouring, bows which are sinew-backed using first-pouring stock as the most durable.
This quick method does not yield as much sinew glue than usual.
First pouring you may want to start with more sinew than usual.
Pour the light syrup through a fine-weave cloth to filter (discretionary). Then pour into wide trays or plates and let jell. Pour about 1/2" deep or less.
You now have a large petri dish. Bacteria may convert your glue to smelly ooze. Wait a few hours until the entire jell is firm but jelly-like throughout. Then pour into wide trays or plates and let jell. Pour about 1/2" deep or less.
Keep cool and out of the sun to prevent melting. When hard and dry, store out of reach of mice and mice. If kept dry, its shelf life is unlimited.
If you misjudged the glue's pre-poured viscosity – if the glue is too watery – it may not jell rigidly enough to hold its shape for cutting. A half-hour in the refrigerator will fix this.
To use, soak the much-shrunken dried granules in sufficient cold water to cover. Wait a few hours, until they are plump and jelly-like throughout. Heat to 160 degrees and stir until uniform, then let cool to a working temperature of 110 to 140 degrees, depending on the materials to be glued. If necessary, thin to a medium-light syrup. The glue pot should be kept below 140 degrees. At 175 degrees animal glue will loose over 2% of its strength per hour. Successive remelting also weakens animal glue.
HIDE GLUE. The same process as for sinew. Makes slightly stronger glue. Hide scrapings, a byproduct of buckskin tanning, work well. These hide should be pulverized, since the paper-thin hide scrapings release their glue faster than sinew. Quick-cooked first-pouring hide glue is generally stronger than the other. Otherwise, let the mixture simmer at 170 degrees for ten hours or until the scrapings are no longer diminishing in bulk. Hide tanning and breaking to thin hide scrapings is a chapter in itself. This information is included in the Fall '91 edition of the Bulletin of Primitive Technology.
BONE GLUE. Requires involved acid processing to separate minerals from collagen. Sinew and hide glues are stronger than bone glue, and much easier to make.
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FISH SKIN GLUE. A moderately strong glue, but weaker and more brittle compared to the weakest hide or sinew glue. Old literature reports fish glue as weaker but more flexible than animal glue. Maybe fish were different back then.
Fish glue that I've bought or made is about as flexible as peeling paint. Other home-brew fish glue makers (the world's second smallest minority group) report the same. But it's fun to try different glues, and it is convenient having always-ready liquid glue on hand.
Remove flesh, fat, and scales. Wash the skins. Cut into strips or squares, then proceed as for sinew and hide glue. Fish skin glue does not jell at room temperature, but remains liquid. Pour into trays and let dry down to a medium syrup.
To store as a liquid, add boric acid as a disinfectant.
Fish glue can be dried as a solid: Once the "leather" stage of drying is reached peel the glue free from its tray. When hard and dry, break into small flakes for storage. Like hide glue, dried fish glue has unlimited shelf life.
FISH AIR BLADDER GLUE. Same process as for sinew, hide, and fish glue.
Fish bladder glue jells like animal glue. It is also as strong and flexible. The old literature reports this glue was preferred by composite bow makers. The unidentified bladders I've used yield glue that is slightly stronger than hide glue, and slightly more yellow-amber in cast. Other fish-bladder glue makers (the world's smallest minority group) report the same.
Certain species of sturgeon were preferred in the old days, and this fish might yield stronger glue, but I doubt if there would be a significant difference.
Jeff Schmidt recently completed an Asiatic composite bow which shot a flight arrow 500 paces. He used sinew glue made on his kitchen stove. Jeff does not feel his glue-line thickness or clamping pressures have been idealized, yet his glue did the job. Earlier in this century, composite bows were made with casein glue, vastly inferior to hide glue, yet these bows held together for a while. The point being that stove-top hide glue is awesomely strong, stronger than you will likely ever require, and that there is no need to search the corners of the earth for exotic fish bladders.
SILK GLUE. Hide glue is made of protein. Sinew glue is made of protein. Fish glue is made of protein. And what is silk made of? Protein!
As I dropped the silk into boiling water, the very air was charged with wonder and invention. I tried to imagine the strange and exotic qualities silk glue would have. Very tough, very elastic, pure white, beautiful. This was going to be great.
Six hours later, I looked in the pot and found two things: boiling water, and a pristine mass of perfectly unaffected silk.
