A paper, emulsion, or other substance that can be rendered light sensitive, exposed to a film positive, and developed so that when the exposed emulsion is applied to the surface of a gravure cylinder, the unexposed image areas are soft and soluble, while the exposed, non-image areas become hard and insoluble. The resist, as its name indicates, resists penetration by an acidic etchant, used to engrave the cells into the image-carrying surface of the gravure cylinder, in varying degrees, according to the amount of UV exposure that portion of the resist received. The hardest portions of the resist offer the most resistance to penetration by the etchant, ensuring that engraving does not occur in the non-image areas. Highlight sections of the image also offer resistance to the etchant, and only very shallow etching occurs there. In shadows and solids, however, there is little resistance to the etchant, so cells can be engraved rather deeply. In mid-tone regions, moderate amounts of engraving occur. Resists, formerly carbon tissue, are now produced from photopolymers. See Gravure Engraving. Resists are also used in the exposure of flexographic printing plates. See Plate: Flexography. A resist is also known as an acid resist and an etch resist.