Offset Printing is a chemical based printing process. The ink and the non ink areas both reside on one level of the printing plate.  This means that the areas where the images are located on the page will be repelled by water.  The non image areas accept water but repel the oil based ink. There are two sets of rollers that sit in Wells that collect the ink and water based solution on to the plate.  At this time the water based solution adheres to the non image areas, and the oil based inks reside on the image areas of the plate.  The invention of the rubber blanket allowed for durability and to produce large quantities on a greater variety of surfaces.  Spot colors also known as pantone colors can also be used in the Offset Printing Process.