Air is good for collections, as long as it does not contain sulphurous anhydride, and is neither too dry nor too wet. The ideal moisture content is 40-60% at 18° C. At a lower temperature, saturation-point of the air is too quickly reached and the vapour condenses on the walls. Lighting is also to be studied. Artificial light is better than direct sunlight. Lead-glass windows retain harmful rays, and glassroof lighting is to be avoided. -- AATA