Flexible polyvinyl chloride (PVC) must not be used in conservation or museums; its volatile degradation products can damage other objects. PVC plasticizers migrate to the surface, and can stain, soften, and swell materials. They make coatings sticky, causing coating transfer, metal corrosion, and disfigurations. Phthalate plasticizers commonly used in PVC are also excellent plasticizers for cellulose nitrate. PVC is rigid without plasticizers; most are oily organic liquids of low volatility, although other organic esters can also be used. Several examples of common problems are described in the article. Chlorine-containing polymers and chlorinated rubbers can be detected using the Beilstein Test. Materials testing positive must be avoided. (Several illustrations and references are given, including a source for the Beilstein test.)