objects helps to increase their longevity; it is recommended that metal objects be stored in closed systems with well-sealed doors and drawers with relative humidity between 35 and 55%. Plastics Plastics experience degradation from several factors including light, ultraviolet radiation, oxygen, water, heat, and pollutants. There are no international standards for the storage of plastics so it is common for museums to employ similar methods to those used to preserve paper and other organic materials. A wide range of instruments and techniques can be used in the treatment of plastics including 3-D scanning and printing technologies as a means of reproducing broken or missing parts. Recommended relative humidity for plastics is 50% along with a temperature of 18–20 °C (64-68 °F). Stone Stone objects take on many forms including sculpture, architecture, ornamental decoration, or functional pieces. Deterioration of stone depends on several factors such as the type of stone, geographical or physical location, and maintenance. Stone is subject to a number of decay mechanisms that include environmental, mechanical, and applied decay. Erosion from air, water, and physical touch can wear away surface texture. Carved stone should not be regularly cleaned as cleaning can cause deterioration by opening its pores as well as removing surface features such as engravings, artists' tools, and historical marks. Dirt, moss, and lichen do not usually cause decay to stone but may add to its patina. Wood Wood is a biodegradable, organic material that is susceptible to deterioration from both living organisms and environmental factors. Some ancient wood is recognized for its archaeological value and falls into two categories: dry and waterlogged. The recommended temperature for storage and display of wooden artifacts is 21 °C (70 °F) during the winter months and 21-24 °C (70-75 °F) during the summer months. The recommended relative humidity for storage and display of wooden artifacts during the winter months is 35%-45% and 55%-65% during the summer months. Effective cleaning of wooden artifacts includes waxing, polishing, dusting, and buffing. For the maintenance of the wooden structure of the architectural heritage, fire-resistant coatings can be used to enhance the fire-resistant performance of the structure. See also conservation and restoration of wooden artifacts. Paintings Painting materials include acrylic paint, oil paint, egg tempera, lacquer, water color, and gouache. Conservation techniques for paintings include dirt and varnish removal, consolidation, structural treatments, in-painting, in-filling, and retouching of losses. It is recommended that paintings be stored