PVC card printers use heat to apply dye onto ID card surface. Dye is carried on cellophane foil. When printhead presses the foil against surface of the id card precisely applied heat evaporates dye which is then diffused onto card surface creating an image. The process is called dye-sublimation as the printing agent is being transformed from solid to gas state with liquid state skipped. The technology was introduced in early 1990s and was used mostly in medical imaging and commercial printing due to high cost. Primary advantage of dye-sublimation printing is continuous tone; this feature helps printed image look natural, it gives the impression of chemically developed photograph. Another advantage of dye sublimation technology is image durability. Plastic ID cards are extremely wear resistant and so is the image on it. High quality ID card dye sublimation printers remain expensive due to high cost of manufacturing. Printing process is sensitive for contamination and careful handling of equipment is required. Used ribbon cartridges need to be securely recycled as printed image of the ID card can be read from used cartridge. In consumer segment dye sublimation printers are used in photo development kiosks that can be found in many retail sale locations.