When in 1707 d’Alencé illustrated the principle of measuring the water content of the air by using a putto, a balance and a bale of straw, he is hardly likely to have considered that his putto would one day take on a symbolic significance in the dispute concerning the ‘correct climatic conditions’ in museums and in the matter of loans. In this dispute, which today divides museum staff worldwide, the question arises as to which way the balance will tip. The Doerner Institut intends to make its position clear.Hygroscopic materials, including wood, paper and parchment, from which artworks and cultural items have been made for thousands of years, react to changes in humidity by swelling and shrinking. This not only involves a change in volume on the part of such materials, but also leads in unfavourable circumstances to irreversible deformations, to tears in canvases, to cracks in sculptures, to the opening up of glued joints, or to the corrugation of drawings or prints. If one keeps the relative humidity and the ambient temperature constant, none of these sensitive materials will undergo any change. We can sum it up quite simply: the more constant the climate, the more stable the condition.