When people come into our workshops here at Thakeham Furniture [visitors are always welcome], one of the things that astonishes them is the sight of a traditional ‘glue pot’ containing hide or ‘Scotch’ glue, such have been used in workshops since the 17th century! Scotch glue is an adhesive, similar to gelatin, that is created other by prolonged boiling of animal hide, and it is used hot. It comes in the form of pearls, which are first soaked in water; the technology of the glue pot, however, has moved on: we use an electric double skin device.
Why not use modern, synthetic adhesives? Well, there are several answers to this question. The first, and most important, is authenticity. When working on antique furniture you should never introduce materials that were not around when the piece was first made; for example, we have a wood store of old timber, so that we never have to use ugly modern mahogany in a repair. Scotch was what was used when the piece was made.
The second reason would be strength and reliability. Hide glue also functions as its own cramp. Once the glue begins to gel, it pulls the joint together. Cabinet makers may glue two planks together by using a rubbed joint rather than using cramps. This technique involves coating half of the joint with hot hide glue, and then rubbing the other half against the joint until the hide glue starts to gel, at which point the glue becomes tacky. At this point the plate is set aside without cramps, and the hide glue pulls the joint together as it hardens.
The third reason is convenience – hide glue is very forgiving. It is water soluble, so it can be washed off easily. Haven’t managed to wash every scrap of old glue off before re-gluing an old joint? It doesn’t matter: the new heat of the new glue will soften up the old and they’ll combine nicely. Working on a piece that was restored by a cowboy last time? If they used a synthetic glue you will be cursing them, as anyone who has spent hours picking tiny scraps of Cascamite out of a joint will testify.