Monday, September 9, 2013

Changing Out the Silica Gel

Silica gel is a form of silicon dioxide (SiO2) with an expansive microscopic pore structure that provides a large internal surface area capable of absorbing and desorbing water molecules. It has been widely used as a desiccant for food and other goods since the beginning of the 20th century. Because art objects require a stable environment, the museum world uses silica gel to control the relative humidity (RH) in exhibition cases and in storage. At Kaman Kalehöyük silica gel is used in storage containers to stabilize the RH. The gel is most often used to create a low humidity environment (≤ 30%) for metal objects, because many of the primary deterioration reactions for metals involve water.


An important part of the conservation work at Kaman Kalehöyük is re-conditioning and replacing the silica gel in storage. Some of the granules are doped with a moisture indicator (cobalt(II) chloride) that  gradually changes color from blue to pink when it transitions from the anhydrous  to the hydrated  state.  Pink silica gel is removed from the storage containers and reconditioned in the oven. Once it has returned to the anhydrous (blue) state, the silica gel can be returned to the many storage containers.