Waterless offset (Source: International Paper Company)
Another form of offset printing is "Waterless Offset". Waterless offset uses the concept of differential adhesion to keep image and non-image plate areas separate during printing. No fountain solution is used in this process.
The method used to achieve this type of printing is a silicone coating on the surface of the offset plate. During plate development silicone is removed from the image area of the plate. Silicone is not removed, however, form the non-image areas. The image areas with no silicone now sit slightly below the non-image silicone area forming very shallow "wells" to hold the ink. The ink is formulated to resist adhesion to the silicone but will deposit in the non-silicone shallow well areas.
Ink viscosity is important so several of the ink rollers must be cooled/heated to maintain a constant temperature which in turn will keep the viscosity constant.
Waterless printing has some advantages over conventional offset as colors are more vibrant and the printed image sharper; however, the overall cost is slightly higher. The plate being made with silicone scratch easily so most waterless printing today is done on sheetfed presses.