Adhesives

Materials: Part 1

1: warm animal glue, ready for application (Photo: Nikki Tomkins

Most historical books will use some kind of glue somewhere in the binding to hold it all together, whether that is to adhere the covering materials down or attach the supports to the boards. Often books will break because the adhesive has failed – becoming brittle, cracking, or losing tack. Other times it is the binding materials that deteriorate, and removing them intact requires removing the old adhesive.

Traditionally, animal glue is the most common adhesive used in bookbinding. This is usually derived from the skin of animals, such as rabbits. It turns liquid upon heating, and makes a strong, flexible glue. Over time this adhesive can deteriorate: exposed to heat and fluctuating environmental conditions the molecules can crosslink and turn the glue hard and brittle.

2. Cooking wheat starch paste (Photo: Nikki Tomkins)
2. Cooking wheat starch paste (Photo: Nikki Tomkins)

When new material is used to help reattach the boards during conservation, that too needs to be adhered into place. Introducing new adhesive into a binding is a considered choice: it’s important to choose a substance that is in keeping historically, can be removed if needed, and suits the materials present both old and new. Japanese Jin-Shofu Wheat Starch Paste is used almost exclusively in the conservation of Crouch’s collection. This is a refined version of flour paste, where the starch is separated from the rest of the wheat. Here in the studio, it is made to a 25% w/v in deionized water concentration, and cooked for 40 minutes until sufficiently tacky.  For binding conservation, the paste is kept dry and viscous. This makes it stronger and reduces the risk of introducing too much moisture into old materials. Moisture can darken old deteriorated leather, or weaken parts of the structure.

In the case of the Crouch volumes, this adhesive has been used liberally on the spine and boards to adhere the covering leather. When the board attachment breaks down, it is necessary to separate the original leather from the spine or the boards. This can usually be done mechanically: using a sharp blade or very thin spatula. Sometimes the spine will need to be cleaned of old glue before applying new linings. Animal glue will soften with moisture, and so a poultice is applied that gradually works on the glue without making the paper spine folds underneath too wet. The glue can then be carefully scraped away.

Sometimes flour pastes are also used in traditional bookbinding. This is derived from wheat flour, where heating the flour in water causes the grains to swell and secrete proteins that create the tackiness. You might find it used to adhere a pastedown, or a tipped in paper page. It is generally less thick and strong as animal glue, and can be more useful for the more fragile paper components in a binding – however, both can be found interchangeably on historic bindings.

When new material is used to help reattach the boards during conservation, that too needs to be adhered into place. Introducing new adhesive into a binding is a considered choice: it’s important to choose a substance that is in keeping historically, can be removed if needed, and suits the materials present both old and new. Japanese Jin-Shofu Wheat Starch Paste is used almost exclusively in the conservation of Crouch’s collection. This is a refined version of flour paste, where the starch is separated from the rest of the wheat. Here in the studio, it is made to a 25% w/v in deionized water concentration, and cooked for 40 minutes until sufficiently tacky.  For binding conservation, the paste is kept dry and viscous. This makes it stronger and reduces the risk of introducing too much moisture into old materials. Moisture can darken old deteriorated leather, or weaken parts of the structure.

3. Wheat starch paste, sieved and ready for application (Photo: Nikki Tomkins)
3. Wheat starch paste, sieved and ready for application (Photo: Nikki Tomkins)

By Nikki Tomkins
Project Conservator

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