Some coatings are processed by UV curing for stability. A release liner is a paper (or film) sheet used to prevent a sticky surface from adhering. It is coated on one or both sides with a release agent. Heat printed papers such as receipts are coated with a chemical mixture, which often contains estrogenic and carcinogenic poisons, such as BPA. It is possible to check whether a piece of paper is thermographically coated, as it will turn black from friction or heat. (see thermal paper) Paper labels are often coated with adhesive (pressure sensitive of gummed) on one side and coated with printing or graphics on the other. See also Gloss Paper, is encrusted with smoothness Carbon paper Folding box board Inkjet paper Paperboard Paper machine Paper making Plastic-coated paper Solid bleached board Solid unbleached board Thermal paper Tracing paper White-lined chipboard Waxed paper References Further reading Soroka, W, "Fundamentals of Packaging Technology", IoPP, 2002, Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, Packaging materials Paper Papermaking Chemical processes