Gravure printing is done from large copper cylinders that are electronically engraved with microscopic holes, or cells. The cylinder is bathed in ink, which accumulates in the cells. Excess ink is squeegeed off by a steel doctor blade. Advantages of gravure are long press runs of consistently high quality, which makes it appropriate for packaging. Disadvantages are high costs for the gravure press equipment, and high costs and long turnaround time for cylinder engraving.
Some packaging is printed by offset lithography, which is done from aluminum plates.
Offset lithography is cheaper than gravure, but due to limitations on plate durability, it cannot print run lengths of more than a few million impressions. Flexography is printing from rubber plates. Advantages of flexography include low cost and adaptability to flexible packaging such as bread wrappers. Disadvantages include low quality levels, which are limited by the resolution of the rubber plate, although quality has improved in recent years due to improvements in plate material and laser plate imaging technologies. Process and Spot Color Most photographs printed today are done using process color, printing with three primary color inks which, when blended through varying tint shades, produce a wide gamut of colors.