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HIDE GLUE PRODUCTION - FROM HIDES?
Yes, from animal hides, almost any animal but primarily from cattle hides. This is simply because of the abundance of cattle hides due to the enormous world wide consumption of beef and subsequent tanning of hides for leather. The trimmed hide pieces (too small or irregular shapes to provide useable leather) are shipped to the hide glue plant.
The glue manufacturing process is basically the following:
wash to remove dirt
soak in lime water for 60-90 days
wash to remove hair and lime
neutralize with acid, drain, wash & drain
add water, heat to 110-120 deg. F for 2-4 hours (called an extraction)
drain off the dilute glue solution, evaporate, chill, dry, grind
repeat last 2 steps 3-4 times to extract all of the glue with the temperature
being increased 20-25 deg. F each time.
The process can lend itself to "home brewing" but it is messy and the aroma is found by some to be less than exciting! Your best bet is to buy the finished product from a reliable supplier.
CHEMICAL COMPOSITION
Hide glue is a protein derived from the simple hydrolysis of collagen which is a principal protein constituent of animal hides. Collagen, hide glue and gelatin are very closely related as to protein and chemical composition. An approximate chemical composition for glue is:
Carbon 51-52%
Hydrogen 6-7%
Oxygen 24-25%
Nitrogen 18-19%
Total 100
The molecular weight of hide glue has a wide range from 20,000 - 250,000. The higher the gel strength, the higher the molecular weight.
History of Hide Glue
Nearly 4,000 years ago, the Egyptians were using hide glue for their furniture adhesive. This is proven by hairs found in Pharaoh's tombs and by stone carvings depicting the process of gluing different woods. Hide glue is still in use today for wood gluing and over the years much has been written about the manufacture and use of hide glue for hundreds of other adhesive applications. With the evolution of synthetic (ready to use) adhesives, hide glue has taken a lesser role in industry but has maintained a major role in repair and restoration of antique furniture, reproduction of period furniture, restoration, production and repair of musical instruments as well as numerous other applications.
Most of the hide glue literature was written from the mid 1800's to the mid 1900's, and unfortunately much of this literature has been lost or abandoned.
GLUE. made from the collagen content of hides and skins, particularly of bovine animals, as distinguished from glue made from bones. Hide glue does not include glue made from the skins of fish.
Glue
An adhesive consisting of organic colloids of a complex protein structure obtained from animal materials such as bones and hides in meat packing and tanning industries. Glue contains two groups of proteins: chondrin, which accounts for its adhesive strength, and glutin, which contributes jelling strength.
Animal glue is a protein derived from the simple hydrolysis of collagen, which is the principal protein constituent of animal hide, connective tissue and bones. Collagen, animal glue, and gelatin are very closely related as to protein and chemical composition. Gelatin is considered to be hydrolized collagen: C 102 H 149 0 38 N 31 + H 2 0 = C 102 H 151 O 39 N 31 which gives an approximate chemical composition for glue of 51.29% carbon, 6.39% hydrogen, 24.13% oxygen, and 18.19% nitrogen. There may be minor variations in the composition of collagens from different sources, as well as in the composition of animal glues imparted by variations in processing techniques; however, the composition of glues and gelatins having widely varying case histories are still very similar.
As a protein, animal glue is essentially composed of polyamides of certain alpha-amino acids. It is believed that these acids are not present in glue in the free state, but rather as residues which are joined together by the elimination of water to form long polypeptide chains.
Glue is a polydisperse system containing mixtures of similar molecules of widely differing molecular weights. Because so wide a range of molecular weights is present, the molecular weight of glue is always an average, ranging from 20,000 to 250,000.
Hide and bone glues make up the two major types of animal glue. Hide glue, which is by far the superior of the two, yields a fairly neutral pH in solution, usually in the range of 6.5 to 7.4, although wider variations are possible. Bone glue is generally acidic, having pH values of 5.8 to 6.3. A glue having a high acidity absorbs less water and tends to set more slowly than a glue having low acidity. A glue having a pH greater than 7.0 tends to foam, and has a shorter shelf life than a glue that is slightly acidic.
Animal glues are soluble only in water, and are insoluble in oils, waxes, organic solvents, and absolute alcohol; however, they may be emulsified in water-oil or oil-water systems under proper conditions. One of the more interesting properties of animal glue solutions is their ability to pass from a liquid to a jelled state uponcooling, and then revert to the liquid state upon re-heating.
The important properties of glue include its jelly strength or consistency (gel strength), viscosity, melting point, adhesive strength, tensile strength or elasticity, optical rotation, swelling capacity, rate of setting, foaming characteristics, reactions to grease (whether acid or alkaline), as well as appearance, odor, color and keeping characteristics. Of these, gel strength and viscosity are most often used for determining the grade of a particular glue.
Regardless of the source of the protein, the glue manufacturing process consists essentially of washing the stock, crushing or shredding the bones or hides, soaking in a lime solution to eliminate hair and flesh, boiling to extract the gelatinous material, gelling, and, finally, drying. The resulting hard, brittle sheets of glue are then broken into pieces or flakes, or ground into powder.
Glue as such is much too brittle for use in bookbinding; therefore a plasticizer, such as glycerin, or a less expensive substitute such as SORBITOL, often combined with glycols and tackifiers, are added to improve elasticity and resilience. These so-called flexible glues are usually prepared from high quality grades of hide glue, with the ratio of plasticizer(s) to dry glue controlling the degree of flexibility that is imparted. In addition, glue, being an organic material, is susceptible to mold; consequently preservatives, such as beta naphthol, or the safer phenols, e.g., pphenyl phenol, are added to prevent mold and bacterial growth. Deodorants, such as terpinol, are also employed in commercial glues.
The wide acceptance of glue as an adhesive stems from its unique ability to deposit a tacky viscous film from a warm water solution, which, upon cooling a few degrees, passes into a firm jelly state producing an immediate, moderately strong initial bond. Subsequent drying provides a permanent, strong, and resilient bond.
The use of glue as an adhesive dates from earliest recorded times. Whoever discovered that a strong adhesive could be produced by cooking pieces of animal hide, or perhaps bone, in water has never been ascertained, but archeological discoveries indicate that the
Egyptians used glue more than 4,000 years ago. The practical manufacture of glue can be traced back directly to 1690 in the Netherlands. Shortly thereafter, or about 1700, the English began making glue and established its manufacture as a permanent industry. Elijah Upjohn is considered by some authorities to have been the first to manufacture glue in the United States, in 1808.
In addition to its use as an adhesive in bookbinding, glue is also used for gumming, for tub-sizing paper, and as a general adhesive in papermaking.
The term "glue" is sometimes used loosely in a general sense as synonymous with "adhesive."
Facts About Hot Hide Glue
There are certain basic things one must know if he is to use hot hide glue correctly-for example, isn't it just unflavored Jello? No.
I have hired many different girls to help me in the years I have restored player pianos, and have discovered one fact: They all thought (initially) that they knew how to glue. The fact was, I knew I could teach them everything else, IF I could just teach them how to glue! That was the hardest part of my job.
Knox Gelatin is food grade gelatin, but is not made from animal hides at all. It is made from rendering cattle bones. That means, it is comprised of a particular group of very light proteins which are edible, and which, in turn, were never incorporated in good adhesives. Granted, it has been rendered "pure" edible grade gelatin and as such retains very few fats (greases). It is these fats which go rancid and cause the glue to stink as mold spores from the air begin to multiply in it.
All hot hide glue has some percentage of fat. It goes with the product- even the so called "technical grades." You just sprinkle a pinch of lye into your pot-- the fats are saponified and fall to the bottom, harmless, even when remixed. That takes care of the problem! Buy it at any grocery store. It is the proteins in the hides of animals which are the heavy, strong proteins required for glue!
Hot hide glue makes a chemical bond with (usually) natural fibers. However, there is a grade of glue that will even bond to glass. The weaker the glue's gram strength, the slower (usually) it tends to set up, and the wider tolerance it has for different materials and longer adjusting times. The particular grade used to stick to glass is still such a strong bond that as it dries and shrinks, it chips the glass it sticks to. This is how glass artists create the "chipped glass" effects found in art glass and fancy windows, yet today. Nothing else yet discovered can do the job as well.
Hot hide glues come in a variety of bond strengths, varying from perhaps 60 grams to about 600 gram. The variety that works best in player pianos varies between 120-180 gm. This gram strength is adjusted in the laboratory by relative viscosity measurements, and does not represent a physical test, directly. However, it does relate to a physical joint test perfectly.
The necessity of hot hide glue usage in player pianos is un-debatable. Carpenter glues are totally unsuitable in player pianos for these fundamental three reasons:
1. Any glue which relies on the evaporation and absorption of moisture away from the joint to set and to eventually dry creates a "lacy pattern" in its joint structure, through which air is able to flow unless the joint is securely clamped for 24 hours. In which case, the air tightness will be better, but never perfect. It will rely strictly on a mechanical tightness and mechanical bond between the parts.
2. Carpenter glues cannot achieve maximum tightness by weighting the joint, unless the weight equals or exceeds a typical clamp! And clamping pneumatic joints cause them to "skate." Both the weight of the clamp on the side and the slight asymmetry of the joint area creates side forces which make perfectly aligned flat joints impossible. And because carpenter glues release their moisture into the flat, thin pneumatic boards being glued down- long before the joint actually sets- that moisture creates a slight warpage in many of the pneumatic leaves, which gradually warp and curl the wood, creating more skating and sliding around by the clamp pressure.
3. Carpenter glues are all "plastic" in that they have a property known as "creep" when used strictly for butt joints and flat joints. Unless the wood has been joined and the glue is used strictly to make the joinery permanent, carpenter glue is seldom permanent in any situation that exerts a constant shear force on the joint. Sooner or later, the joint "stretches" to the place that it will fail. For example, when valve blocks are glued with hot hide glue, they stay glued under any amount of spring tension used to clamp them down. But when the same blocks are glued by any carpenter glue, some of them will be found to have their pouch boards displaced from the body of the block about 1/16" in less than a year, simply because the block is pressed into the cork gasket and the pouch board, untouched by the spring, is sliding back from the compression on it by the cork.
There is a fourth reason you don't want to use carpenter glues, by the way. In the case of the yellow glues, you will never get them out of the wood! The joint, albeit a lousy one and a leaky one, will force you or the next person to build new parts! The advantage to these glues is obvious: Even an idiot can get as good a joint as an expert. The disadvantages are equally obvious: The joints are totally unsuitable, inaccurate, cause warpage in some cases, and leak air. Except for those things and the fact that you cannot remove them, carpenter glues are just perfect- for ruining player pianos.
There are 3 main reasons why hot hide glue is perfect, both for wood joinery and for butt and flat joints in player pianos and joints requiring perfect air-tightness.
1. Hot hide glue sets, not by water evaporation thresholds, but by cooling off a bit, and gelling! When this kind of glue sets, it gets a "death grip" on the parts, preventing them from sliding, so actually, only weighting is required, and just enough weight to squeeze excess glue out of the joint. The parts won't "skate." That allows one to find about a dozen lead weights of about 1 lb apiece (or somewhat less) and rotate them leapfrog through the entire range of pneumatics. Once the glue has set, the weight is no longer required.
2. Hot hide glue dries with a 100% chemical bond on the parts, creating a perfectly airtight seal, as long as the glue consistency (which is adjustable-another great advantage) is adequate and the joint in full contact when the parts were initially placed together. As with any glue, it is possible to create a leaky joint. But with hot hide glue, due to the gell setting factor, it is possible to make every joint as perfectly air tight as every other joint, while with carpenter glues, this is just not possible.
3. Hot hide glue becomes permanent and brittle. It has zero "creep." It exists in oriental furniture and chairs yet today, which still, after a thousand or more years of usage, have perfect joints. That, friends, is what anybody would call "great glue!"
There is a fourth reason to use hot hide glue as well: It can be removed! Moisture or steam along with heat will eventually loosen animal glue, unless certain additives are used which are able to render animal glue waterproof! So, in the course of your rebuilding, you will very likely have to get back into some of your work. You should be comforted to know that with animal glue, you still can! With carpenter glues, you cannot.
To test your glue, your best test, of course, is to glue up 1" wide strips of wood with a 1" square flat joint between them. When fully dry, weight until the joint breaks, record your break strength. From that time on, you will know what you have with that particular batch of glue. Try thin and thick mixtures of it, too, and test to see if you are really getting the strength you need to have. Hot hide glue should be stronger than carpenter glues, as well. At least, it has the capacity to be stronger.
To test for glue quality before bonding, use one ounce of glue* per pound of water*". Wait 12 hours for the glue to take up the water, fully. If the glue appears dissolved into the water, it is no good. If, when you pour off the water, the glue stays coherent to a degree, this is useable as glue. Now, weigh the mass of jelly glue. If it weighs 5 times or more its initial weight, it is excellent glue. And the solidity and coherency of the mass will tell you how strong it is going to be!
* One Ounce of Glue equals about 2 Tablespoons
*" One Pound of Water equals about One Pint
You see, hot hide glue contains many different kinds of protein. The strongest and best proteins are also the heaviest and most cohesive, as you might expect. So when you start using your glue the next day, stir the pot, because your best and heaviest glue has settled to the bottom. Definitely not the stuff that Knox Gelatin is made of.
Understand one very important fact about hot hide glue: It reminds one of using solder. The joint must be made hot, and after a quick, initial positioning, cannot be moved while the solder is going through its phase change to partially solidify, or you will have a "cold solder joint." It looks all right, but crystallizes and breaks loose.
So does hot hide glue, and that is why it takes a bit of getting used to. That is why I suggest cutting some scrap wood and playing with it. Write on the pieces you are doing, what it was that you did. Then break them off. If you cannot tell any difference between different methods, consistencies, and timing, you are not testing correctly.
As another test, be sure to include sizing a board with thinned down glue before gluing
up. Sizing decreases the glue's latitude to be moved because it shortens the placement time before gelling and setting, so it greatly facilitates placing down pneumatics by speeding up the "death grip" if you have already a system for placing pneumatics accurately. Sizing also acts as a way of increasing the strength of your glue when used properly. So if you happen to have some cheap grade of hot hide glue, you can still use it if you size first.
One last note is, on any new wood in which end grain is to be glued to, as on pneumatic covers, BE SURE to size the end grain and let it dry before trying to glue anything to it.
Once you get accustomed to using hot hide glue, you will wonder how anybody could fall for bottled glues! That stuff is really a waste of good shelf space in a player shop.
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