Large libraries, art galleries and museums have considerable proportions of their collections in storage areas inaccessible to the general public due to the cost of display space, operating costs, and the need to adequately protect their holdings from damage or theft. As a result, ever smaller proportions of cultural heritage are actually suitably displayed to permit casual browsing, and in many libraries browsing is no longer possible. Each item must be specially requested on the basis of prior knowledge of its existence.