However, extreme changes in temperature and humidity can cause chemical and physical damage. Typically museums strive to store ceramics, as well as many other material types, in a stable temperature of 68 °F with ± 3°. Additionally relative humidity should be stabilized at 50% also with a ±5%. Storing objects near windows, heaters, fireplaces, and exterior walls can create an unstable environment with temperature and humidity fluctuation and increase potential for damages. Some storing materials can be harmful to ceramic objects. Wool felt attracts and harbors insects including moths and silverfish which can be potentially very harmful to other collection material types. Polyurethane foam deteriorates over time which leaves a by-product that are sticky and acidic. One of the cardinal rules in object handling is to treat every object as if it is fragile and easily breakable. Museum technicians, curators, and conservators are trained to prepare a moving plan before an object is even touched that way minimal damage can occur when handling or moving an object. In the museum field is it a known fact that a vessel, or any object, should be held and handled by its strongest part, such as the base, and with both hands. Areas such as the handle or neck of a vessel tend to be the weakest points and may break if picked up by these components. Damages also occur to ceramics from previous restoration. Although the intent was to repair the object for use or display, some dated practices are now known to increase damages either physically, from rivets or staples, or chemically, from old used adhesives that off-gas. Overpaint is a technique that is used to cover imperfection on the surface of a ceramic piece. Differences can be seen to the naked eye due to discoloration, being matched poorly, and change in texture or gloss. subtle difference can also been seen by restorers by using lighting and magnification. Overpaint and surface coatings can be removed either mechanically or with the use of solvents. Mechanical removal of overpaint include physical techniques to remove the coating from the surface. On a glazed surface a sharp needle or scalpel can be used. If mechanical removal is not possible without damaging the surface then solvents can be used instead. The archetype solvents typically used are water, white spirit, industrial methylated spirits (denatured alcohol), acetone, and Dichloromethane which is usually found in the form of a commercial paint stripper.