Thursday, September 17, 2009
Have you ever noticed how certain recipes always ask you to pat your poultry or fish down dry after rinsing it with water? We do this exercise but why? The reason for this is because oil and water just don't mix. If you wash a piece of chicken by running it through water and do not dry the chicken before adding oil, the water will repel the oil. If you pat the chicken dry it will be more receptive to absorbing the oil and you will achieve a nice coating.
This same concept, that oil and water do not mix, is the main principle behind offset printing. The poultry in printing would be your plate. Not to be confused with something you put your food on, a plate is a metal sheet that attaches to a cylinder on press.
The plate contains the actual dotted image that will be printed for each color we use (CMYK). The plate’s image area contains chemicals that are highly receptive to oil based inks but naturally repel water. When we attach the plate to the cylinder on the offset press, the plate will rotate and come into contact with dampening rollers (water) and then ink rollers (oil). The water dampens the plate and when this happens the oil receptive image area will repel the water, while the non-image area will receive the water. When the plate comes into contact with the oil based ink, the ink will only adhere to the oil receptive image area and it can not adhere to the non-image area because that part of the plate is coated with water. Because plates do not transfer the cleanest image to a sheet of paper, the inked image is then transferred (or "offset") from the plate to a durable rubber blanket that conforms to the surfaces of all types of paper stocks. The blanket prints the image to the paper completing the process of offset printing.