Hide glue is simply collagen. A good model for collagen is to think of one of those coiled up plastic scrubbers. When it is heated with water, the chains of molecules that make the spring like coils become soft and untangle themselves in the water solution. When they dry back out the molecules coil back up locking tightly back together. Collagen glues are water soluble as well as heat sensitive. Under ideal conditions (dry environment with moderate temperatures) it is reputed to be one of the strongest glues available even by modern standards. Hide glue is often used by scribes, as well as other artisans.
Hide glue is extremely easy to make, using items commonly available in your kitchen and local store.
- Cow hide from dog treats – the whitest and cleanest you can find.
- Heat source – crockpot, hot plate or stove.
- Pot or large coffee can to simmer the solution in.
- Pans and trays to dry your glue on.
- Airtight jar to store dried glue.
- Assorted kitchen utensils to stir and strain.
The rawhide chips I used were cut into about 2 inch squares and were practically white. Both Theophilus & Cennini say the material used for glue should be well washed, with Theophilus specifying the hide is supposed to be clean and well scraped. That means the flesh and hair should be completely removed. The white chips I used needed no further processing to fit this description. It is worthy to note that there are many other hide based dog treats that are much less “clean”, and would not be appropriate for making glue. Certainly rawhide treats with added flavorings should be avoided. I made my glue years ago, but these appear to be similar products.
You should be able to purchase this type of item in your local grocery or big box store, at a reasonable price. If you prefer to shop online, this is the type of thing you are looking for.
- Hartz 81271 1 Lb DentalTM Rawhide Chips
- Savory Prime Rawhide Chips, 4-Ounce
- Exer-Hides Rawhide Chips (only available in the store)
- Dog treats were put into the can, covered with water, and let sit over night to hydrate. This makes them feel like a thick rubbery piece of skin. This is in keeping with Cennini’s recipe – Chapter 110.
- The next day, I turned on the hotplate and started to heat them. Keep the heat low as Theophilus says don’t boil (but Cennini says boil). I had read somewhere that the ideal temperature is between 140 and 170 degrees Fahrenheit. At higher temperatures, the collagen fibers are broken down into shorter protein chains. Shorter fibers means weaker glue. However, Cennini uses the word boil and boiled down. I was very successful with low heat and patience.
- As the rawhide treats slowly dissolved I poured off and strained the liquid into a fresh clean can. I then added more clean water to the rawhide pieces, and started a second hotplate to continue the evaporating process of the strained liquid. I kept the strainings from each successive batch separate. The best, strongest glue is supposed to be the least cooked. Also it will be the clearest.
- As the glue cooks slowly down, it starts to get sticky making your fingers stick together when it cools just as Theophilus describes. It was at this point I figured it should be reduced to half, meaning further cooking until half the volume remained.
- Once this cooking and reducing was done I poured it into glass backing dishes about 3/8 inch deep. The glue sets up like jello but a little stiffer.
- I then cut it into about 3/8 inch cubes and let it dry. ( At that time I didn’t have the recipe that said to cut it like slices of bread.)
- When they were about half dry and rubbery I scraped them out and set them on trays to finish drying. I did this whole process with each successive pass of straining and water addition keeping each batch separate.
The glue making process took about a week. By that time there was nothing left to the dog treats but about a tablespoon of fibers that looked like gummed together carpet fibers and they would not dissolve in the water.
After drying the little glue cubes, It easy easy to see the difference in the various runs. The first batch was almost clear, the second a light yellow but still very transparent. The subsequent, middle, batches started getting a milky cloudy color. The final batches were white/beige and opaque. The well dried cubes of hide glue will store indefinitely, if the jar is airtight.
Using the Hide Glue
To use the hide glue, rehydrate the cubes in water while heating. For the small amounts needed for scribal purposes, or other small projects, we have a soapstone oil diffuser. A tea light candle goes underneath the small bowl, drop in 3-6 cubes, and cover with water. I stir occasionally, and will add more water as needed, until the cubes are fully dissolved, and the glue is a spreadable consistency. Once I am done, I may continue heating the glue to dry it back out, or just let it air dry.
Eleanor has used my hide glue diluted as a size for handmade paper, and with some failed attempts to use gold leaf. Sigurd used hide glue to glue the two layers of leather together on his archer’s bracer. (That was a risky decision, because if the archer sweats, the hide glue could come loose. But he was so excited about the chance to use a period-correct glue.) Eleanor also used the hide glue to secure layers of her needlecase.
I’ve included several of the pertinent glue recipe, and encourage you to follow up and read more. It is in reading multiple recipes that you learn the basic process, which is nearly the same, regardless of the source of the collagen.
Chapter 18. Glue from Hide and Stag Horns
When this has been carefully dried out, take some cuttings of the same hide [horse or ass or cow], similarly dried, and cut them up into pieces. Then take stag horns and break them into pieces with a smith’s hammer on an anvil. Put these together in a new pot until it is half full and fill it up with water. Cook it on the fire without letting it boil until a third of the water has evaporated. Then test it like this. Wet your fingers in the water and if they stick together when they are cold, the glue is good; if not, go on cooking until your fingers do stick together. Then pour this glue into a clean vessel, fill the pot again with water, and cook as before. Do this four times.
(A Fish Glue from) Chapter 28. Milling Gold for Books; and Casting the Mill
…Now take the bladder of the fish called sturgeon, wash it three times in warm water, cut it up in pieces, put them into a very clean pot with water, and let them soften overnight. On the next morning cook them over the fire without letting them boil, and test them with your fingers to see if they stick together. When they stick fast, the glue is good.
Chapter 31. All the Kinds of Glue For Gold Painting
If you do not have a bladder [of sturgeon], cut up thick calf vellum and wash and cook it in the same way. You may also cook in the same way the bladder of an eel, after has been very carefully scraped, cut, and washed. You may also three times cook the bones of the head of a pike, after they have been carefully washed in hot water. Whichever one of these you have cooked in this way, add to it a third part of the very transparent resin and cook it lightly; then you will be able to keep it as long as you wish. – Theophilus – c.1100.
300 years later –
Chapter 109- How colla di caravella is made, how tempered, and for what purposes it is used
There is a glue called colla di spicchi, which is made of the clippings of the muzzles of goats, feet, sinews, and many clippings of the skins. This glue is made in January or March during the great, cold or high winds, and is boiled with an equal quantity of water until it is reduced one-half; then pour it into flat vessels, such as saucers for jelly, or basins. Let it remain one night; the next morning cut it in slices, like bread, with a knife; put the pieces on rush- mats to dry in the wind, without sun, and it will become excellent glue. This glue is used by painters, by saddlers, and by many masters, as I shall thereafter tell you. It is good glue for wood, and many other things, of which we shall treat fully when showing how it is to be used, and in what manner for plaster, in tempering colours, making lutes, in inlaid works (tarsie) also to fasten wood, and the leaves (of books), in tempering plaster, in working with plaster in relief, and it is useful for many things.
Chapter 110 – A perfect glue (size) for tempering the gesso for panels (pictures).
There is a glue made from waste of sheep and goat parchment, and from the clippings of this parchment. These are to be well washed, and put to soak for the space of one day before they are boiled down. Boil them till the quantity of water is reduced to one-third part; and I wish that, when you have no colla di spicchi, you should use this only for mixing with the gessos for your panels, and it is impossible any- where to find better. – Cennini – c. 1400
The newer translation, by Thompson, gives ‘goat glue’ for colla di caravella, and ‘leaf glue’ for colla di spicchi. Thompson also adds mention of straining the glue. While I can’t analyze the minor translation differences, observation of the glue showed straining was essential to a smooth glue.
Cennini’s recipe specifically calls for goat parts but the process and the end product doesn’t change much for different glues made from different animal sources. The footnote in Thompson’s translation suggests that there is some confusion about what is meant by “reduced to less than half.” Having made hide glue and processed it for storage in a similar (dried) manner, I would interpret Cennini’s process to mean reduced to half the volume starting with the proper strength for ready to use liquid glue.
In general Theophilus’ recipes seem to be more complete that Cennini’s but in the case of collagen glues only Cennini tells us how to make “leaf glue,” which simply put it is dried out hide glue. While it takes several days to make a full batch of animal glue, and several more to dry it out to leaf glue, it only takes five or ten minutes to redissolve it once all the other processing has been accomplished. Cheese-lime glue may take more than an hour to make and it must be made fresh from scratch every time. When I made leaf glue I did not slice it like bread but cut it into little pieces like ¼ to 3/8 inch dice and dried it that way. I suppose Cennini might have called it bead or dice glue if he has made or purchased it that way?
- Theophilus, John G. Hawthorne, and Cyril Stanley Smith. 1963. On divers arts; the treatise of Theophilus. [Chicago]: University of Chicago Press.
- Cennini, Cennino, and Daniel V. Thompson. 1954. The craftsman’s handbook. New York: Dover Pubications. (modern edition, quite afforable.)
- Quotes taken from CENNINI, and C. J. Herringham. 1899. The book of art Cennino Cennini. A contemporary practical treatise on quattrocento painting. Translated from the Italian, with notes on media︠e︠val art methods. London: G. Allen.
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