Humidity and Temperature

The use of silica gel

Individual display cases can act as buffer zones, and maintain humidity at reasonably constant levels—provided the temperature does not vary greatly. However, fluctuations can occur and it is sometimes necessary to use buffering materials: silica gel, for example.

Silica gel is often seen as a simple solution to environmental problems. In some museums and galleries, small bags of silica gel are placed in display cases and left there permanently. Unfortunately, this has almost no effect.

Using silica gel is not simple. The calculation used to determine the amount of silica gel required is complex. It involves a knowledge of the daily rate of air-changes in the case, the local humidity conditions and the volume of the case.

The amount of silica gel required is far more than most people imagine. The amount required can range from approximately 7kg/m3 to about 20kg/m3, depending on conditions. This is a lot of silica gel.

The dish of blue silica gel is ready for use. It will absorb moisture and so remove water from the atmosphere. When silica gel has absorbed all the water it can, it turns pink. When the silica gel is pink, it needs to be reconditioned Photograph courtesy of Artlab Australia

Silica gel also needs to be reconditioned, because it absorbs water and retains it. The silica gel has to be removed from the case and reconditioned—usually by heating in an oven—and then put back in the case. You may need two batches of silica gel, so that when you are reconditioning one, the other is in the case.

Display cases that are to contain silica gel should ideally have separate compartments: one for the object and one for the silica gel; and there should be air flow between these compartments.

If you have a problem relating to temperature and humidity and how to manage it correctly for the preservation of your important objects, contact a conservator. Conservators can offer advice and practical solutions.