May 3, 2006

A Formula for Gum

The glue that is used for gummed labels comes from the bones and hides of animals. It can be laid down on one surface and dried, ready to stick to another surface when moistened. The ability to become sticky when wet and nonsticky when dry in a reversible way is the reason this adhesive is used on envelopes, stamps, and labels.

Materials and Equipment

• 1 packet unflavored gelatin1 tablespoon cold water
• 3 tablespoons boiling water
• 1/2 teaspoon corn syrup
• small bowl
• spoon
• clean paint brush
• pieces of paper, clippings, etc.

Procedure

Sprinkle the package of gelatin over one tablespoon of cold water. It will swell and soften in about ten minutes. When it is soft add the 3 tablespoons of boiling water and the corn syrup. Stir until it is dissolved.

Paint the mixture on the pieces of paper. Let dry. To use as an adhesive, moisten the dried surfaces and stick them on other pieces of paper.

Observations and Suggestions

Gelatin is a protein manufactured by heating animal connective tissue, such as skin, tendons, and ligaments, with acid. It will not dissolve in cold water but will swell as it absorbs it or when in contact with it. It will dissolve in hot water, and when a gelatin solution cools, it traps the water in its structure, giving it a semi-solid structure. Your gelatin adhesive will gel when cooled, but you can turn it back into a liquid by heating it again over hot water.

The old-fashioned animal-hide glue is a poor grade of gelatin made by cooking bones and hides in acid. It is then dried and ground, and sold in a powdered form. One of our source books said that you could tell a good grade of such animal glue from a poor one by the amount of water it absorbed. The more water the glue absorbed, the higher the quality of the glue (and the more refined the gelatin in it). Animal-hide glues have to be heated to be usable and applied while still warm. They harden to form an extremely strong bond and are used for wood furniture.

See if you can improve the adhesive qualities of your gelatin glue by adding a teaspoon of vinegar (an acid) and heating it for a few minutes. Be careful not to let the water evaporate completely. Add water as needed to keep the level the same. Compare the strength of the bonds.

Reprinted with permission from The Secret Life of School Supplies by Vicki Cobb. Published by J.B. Lippincott, New York. Text copyright © 1981 by Vicki Cobb (www.vickicobb.com).

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