I’ve done extensive research and have written several articles on this glue. I thought that’s all the information there is until I met Eugene. He was kind enough to release a 15 page dossier on this glue. He’s been working with and selling hide glue since the 50s and he has summarized and simplified the information of the last 70 years of working knowledge in 15 pages. Make a cuppa, sit back and have a read. I will not post all 15 pages in one post, but will do so in several posts over several days.
BY: EUGENE B THORDAHL
“40 Centuries Old And Still Holding”
Nearly 4,000 years ago, the Egyptians were using hide glue for their furniture adhesive. This is proven by chairs 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.
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 110-120o 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 20-25o 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.
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:
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.
TESTING HIDE GLUE AND STANDARD GRADES
Peter Cooper, founder of the domestic glue industry in the early 1800’s, is generally credited with developing the standard methods of testing and grading glue. The standard is recognized worldwide. The main components are viscosity and gel strength (or jelly strength which is measured in grams).
The viscosity and jelly determinations are made on a 12.5 percent solution of hide glue, employing 15 +/- 0.01 g of commercially dry glue with 105 +/- 0.2 g of distilled water at 25o +/- 2o C using a standard 150 ml test bottle. The viscosity is determined by timing the outflow of 100 ml of the glue solution at 60.0o C from a calibrated glass pipette under closely controlled conditions. The millipoise value is determined by proper reference to the time of outflow in seconds and the constants of the specially calibrated pipette. The jelly value in Bloom grams is obtained by subjecting the viscosity sample to rigidly controlled gelation in a water bath maintained at 10o +/- 0.1o C for 17 hours, followed by measurement of the force in grams required to depress the surface of the glue jelly 4.0 mm by a mechanically loaded plunger approximately 0.5000 inches in diameter, using the Bloom gelometer.
A chart of Standard Grades follows. Note the glue grade designation is the “Standard Mid-Point Grams”.
Standard Hide Glue Grades
|Standard Mid-Point Grams||Range Grams||Standard Millipoise Value||Range Millipoise Value||Peter Cooper Grade Designation|
|315||299-330||111||102-112||1 Extra Special|
Moisture: 10 – 15%
pH 6.0 – 7.5
Form Dry Granular 8 – 10 Mesh
Color Yellow/Amber to Brown
Specific Gravity 1.27
A later discussion will present the value and reasons for using different grades. Generally, the higher the gel strength (in grams):
- the higher the molecular weight
- the higher the viscosity
- the faster the tack and set
the shorter time you have to complete a lamination