Rylands BlogConservator’s Caviar: Isinglass Preparation

In January, the conservation team prepared some purified isinglass. Isinglass is a type of glue made of fish, more specifically the dried sturgeon swim-bladder membrane. This adhesive offers different qualities for conservation treatments, such as good ageing properties, flexibility and light fastness. Isinglass is widely used for conservation treatments, for example the consolidation of pigments, repair of parchment or prepared as remoistenable repair tissue.

Figure 1: Weighing isinglass

However, isinglass can’t be used in its raw form. Starting with sheets of the fish membrane, the isinglass must be dissolved, purified and prepared in a form ready to use. The full procedure takes approximately 3 days.

After weighing the desired amount of dried glue, the sheet is carefully cut in small pieces of a few millimetres length. The pieces are covered and left to soak overnight in deionised water.

Figure 2: The membrane is cut out in small pieces

The glue is then sieved, gently massaged then, divided into equal parts, and put to dissolve in fresh deionised water. The water is gently warmed in a bain-marie at 29 degrees, and frequently stirred up to facilitate the dissolution. At higher temperatures, the gelatine of the glue starts to degrade and its structure and properties are then altered.

Figure 3: Sieving and dividing the soaked glue in equal parts

Figure 4: Dissolving in a 29 degrees bain-marie

When the dissolution is completed, the isinglass is sieved twice through a thin muslin cloth to remove any impurities. The discs can then be prepared!

Figure 5: Second sieving through a muslin cloth

Figure 6: Preparing the discs using pipettes

Using pipettes, small drops of glue are carefully spaced out on a sheet of Melinex^©.

Figure 7: Isinglass drops on Melinex©

The drops need to dry whilst covered, protected from dust and impurities. This takes usually between 12 to 24 hours depending on the weather conditions.

Figure 8: Drying under a plastic cover

The discs can finally be peeled out of the Melinex and stored in a jar.

Figure 9: Isinglass discs ready to use

Figure 10: Isinglass discs ready to use

The discs are now ready to be diluted in water, warmed up in a bain-marie and used as an adhesive in a conservation treatment. Keep an eye out for our next blog to see it in action!