dryness resulting in cracking and breakage, fading from exposure to light, mold resulting in odors, stains, and distortion, and insects and dust, both of which can cause holes and abrasions. Corrosion can also occur when leather comes into contact with metals. There are two primary methods for leather conservation: application of dressings or treatments to prolong the life of the leather and improving the means by which leather is stored. The second method is a preventive approach while the first, an older method, is an interventive approach. Leather artifacts are best stored with relative humidity between 45% to 55% and a temperature of 18-20 °C (64-68 °F). Glass and ceramics Glass and ceramics can be maintained for much longer periods of time and are two of the most durable materials. The biggest risk to glass and ceramics is breakage, however improper display and storage can lead to stains and discoloration. Ceramics can become stained from inappropriate cleaning and repair while porous or cracked ceramics can develop stains from being soaked in water during cleaning. Increased temperatures can cause darkening of already existing stains and can lead to cracks. Glass can become damaged from 'weeping glass' wherein droplets of moisture form on glass surfaces. This can lead to a leaching out of unstable components that produce an alkaline solution. If allowed to remain on the glass for an extended period of time, this solution can produce fine cracks known as crizzling. Careful handling and storage is the surest means to preventing damage to glass and ceramics. The below table displays recommended storage conditions for damaged and unstable objects: Metals Metals are produced from ores that are found naturally in the environment. Most metal objects are made from a combination of individual metals called alloys and exhibit different strengths and colors based on their composition. Metals and alloys commonly found in cultural objects include gold, silver, copper, pewter, tin, and iron. The most common form of deterioration for metal is corrosion. Corrosion occurs when metals come into contact with water, acids, bases, salts, oils, polishes, pollutants and chemicals. Mechanical damage, breakage, dents, and scratches can occur from mishandling metal objects and result in damage to the metal object. Over polishing can lead to deterioration and potentially misidentification by removing plating, decoration, makers' marks, or engravings. Mechanical, electrical, and chemical interventions are often used in the treatment of metals. Appropriate storage of metal