Several types of printing processes exist throughout San Diego County. Each type of printing process typically involves unique products, equipment, inks, solvents, application methods, and drying procedures. The most common process types are flexographic, gravure, silk-screening, lithographic heatset, lithographic nonheatset (newspaper), and letterpress. All printing operations emit some volatile substances into the atmosphere by evaporation. Actual emission rate are, however, highly dependent upon process type.