This technique begins with a highly polished, beveled plate of pure copper, which is sprayed or dusted with asphaltum or rosin -- acid resist materials. The plate is heated so the resist sticks. A positive transparency must be made from the film negative, then printed on a gelatin-coated paper called carbon tissue. The gelatin on the treated paper becomes harder when exposed to light, creating areas that will not melt easily. The image is transferred to the plate, and the softer gelatin is washed away with water. Then the printmaker etches the plate with ferric chloride, creating tiny pits in the surface that correspond to the thickness of the gelatin. The result is a finished printing plate.
Traditional photo etching provides an easier technique than photogravure. It uses a light sensitive plate made from zinc, with a positive transparency attached. The plate is then developed in a dyed acetone solution, rinsed, and placed in an acid bath. The acid bites into the exposed areas of the plate, creating recesses. Once the plate has been rinsed and dried, it is ready for printing.
Solar plate etching uses a light sensitized, steel-backed polymer plate, and requires no solvents or acids. The process involves exposing the plate to the sun while in contact with a positive transparency. Then the plate is developed in water and scrubbed. This technique is the simplest and the least dangerous, but does require a specialized plate, and is more expensive than traditional etching or photogravure.