The conservation of glass, as of all artefacts, falls into two main categories: passive conservation, the control of the surrounding environment to prevent further deterioration; and active conservation, the treatment of artefacts to stabilize them. A storage or display environment will consist of one of the following: (i) natural climatic conditions (especially painted glass windows and glass mosaics in situ); (ii) modified (buffered) climatic conditions in buildings and cases with no air conditioning; (iii) controlled climatic conditions, where air conditioning has been installed in museum galleries or individual showcases, to hold temperature and relative humidity within carefully defined parameters
