Relative humidity

Relative humidity is a measurement of the amount of water in the air. It is important to collection managers because the objects in our collections respond to relative humidity. Organic collections (things like paper, cotton, ivory or silk) will absorb and desorb moisture from the air resulting in a matching change in their moisture content. When organic materials have a higher moisture content they will swell and this may result in a physical strain especially if they are restricted: for example, a picture frame is restrained at each corner, or planks in a table are restricted by their alignment to the next one. Hight moisture content will make organic materials more tempting to many insect pests and whilst some moisture content is good to ensure flexibility too much may lead to the object being vulnerable to physical damage – think how delicate wet paper is. Inorganic materials like glass or metal, have a different relationship with moisture in the air. Most inorganic have very specific conditions in which they are stable or unstable. High humidity often plays big part in their decay processes, for example think about how iron rusts faster in damp conditions. Other inorganics are surprisingly vulnerable to incorrect humidity, glass can weep, fossils decay or salts dissolve and recrystallize causing damaging splits

Introducing the agents of deterioration

The agents of deterioration (AoD) is a tool developed by the Canadian Conservation Institute (CCI). Inspired by risk management, the AoD can provide those responsible for collection care with a checklist of things that can cause loss to their collections