The extent of lending among museums and private collectors has increased enormously in the past few years. Objects, which for centuries remained in houses, churches and monasteries in a stable environment, are now circulated between museums and exposed to extremes of heat, cold, moisture or dryness. Panel paintings, ivory, delicate woodcarvings, glass, textiles, leather and paper are among the materials most susceptible to changes in humidity. In addition to the inherent dangers due to the physical nature of fragile and sensitive works of art, there is the risk of entrusting them to untrained helpers, working under pressure of deadlines. In spite of every precaution, there is the hazard of human error in handling and packing. Exposure to spotlights and to the fading effects of too much ultra-violet component in sunlight or fluorescent tubes is also to be avoided in the display of textiles and watercolors.