Hide Glue

Hide glue is an adhesive made out of the connective tissues, bones and hides of animals (mainly cattle) that have gone to the slaughterhouse. It is extracted by "cooking" raw stocks to obtain glue liquors that are filtered, evaporated to glue solids and then dried before grinding. When you buy hide glue, it comes in hard yellow-orange granules or pellets.

USES OF HIDE GLUE: Hide glue has plenty of uses. You can apply it to regular joinery. Numerous tests conducted by woodworking magazines have shown that the bond hide glue makes is more than adequate to hold a joint together. Apply the glue with a stiff brush and join the pieces while the glue is still hot. As the glue cools, it will gel quickly and lose its adhesive properties. However, it will reactivate if more hot glue is added, or if the joint is heated.

PREPARATION: To prepare hide glue for use, you have to soak the pellets in cold water for several hours until they soften and become gelatinous. If you've never used hide glue before, it is best to start with a small batch. Put three tablespoons of dry glue in a heat- resistant glass container (most food jars work well) and cover with two tablespoons of water. A larger batch of glue can be made using the same proportion of glue to water. Next, place the gelatinous glue mixture into a water bath. Heat the water to 140F. Be sure to use a thermometer, as it is important to maintain this temperature, DO NOT GO OVER 140F. DO NOT BOIL. If the water gets too hot, it will overheat the glue and cause it to lose strength. It is a good idea to stir the glue mixture occasionally to help work out any lumps but it is not absolutely necessary. After a few minutes, the pellets will be melted and the glue will be ready to use. A properly prepared and heated batch of glue forms a steady thread as it drips from a brush back into the glue pot. If the glue drips from the brush in droplets, it is too thin. To thicken it, stir the glue while it is being heated until sufficient water has evaporated from the mixture. If the glue forms thick clumps on the brush, dilute it with hot water until the desired consistency is achieved.

Bloom Strength Comparison:

Glues recommended for water gilding can be compared by evaluating their gel strength as defined by the Bloom Gelometer which is a measure of the rigidity of the glue. The Bloom unit is a measure of the force required to create a 4 mm depression on the surface of a sample prepared using a specific formula. High Bloom units indicate a more rigid and stronger glue. Lower Bloom units indicate the glue is more flexible and weaker.

Preparing Gilder's Glue:

A two-step process is required when working with natural glue products. First the glue particles are soaked in cold water to soften and swell the material without dissolving. This may take several hours or overnight. Then, the soft glue is gently heated to completely dissolve the material. All glue solutions will spoil over time and will lose their adhesive power. It is best to store prepared glues in a cool dry place or to refrigerate. Recipes for making gilder's glue vary widely and experimentation will lead to the perfect formula for your specific needs. Temperature and humidity will affect the performance of glues and seasonal changes to recipes may be required. Gilders may vary the glue/water ratio, the temperature/time dissolving process, and may mix Hide and Rabbit skin glue to create the perfect material to create a superb water gilded surface.