In the field of art conservation the terms archival, inert, stable, safe, etc. refer to materials or processing methods that are expected to allow items to be stored for extended periods of time without loss of quality. These materials should not degrade over time and should not contain volatile materials that will be emitted from the material, or ‘off-gas.’ Both degradation products and off-gassing materials can do serious damage to some art materials. Metal, paper, and shells are examples of sensitive materials that can be damaged irreversibly from proximity to ‘unsafe’ materials.