You might assume that all commercial printing ink is the same. In fact, both the composition and use of printing ink involve a lot of nuances.
For now, let’s start with two general rules to keep in mind. Printing inks differ depending on the equipment in which they will be used and on the intended use of the printed product.
The technology with which ink will be applied might include offset printing and digital printing, for instance.
Offset lithography “works” because oil and water repel each other. (You can test this for yourself by pouring both water and olive oil into a glass.)
Offset printing ink is an oily substance that is chemically produced to seek the image areas of a printing plate while avoiding the non-image areas, which are coated with water. In an offset printing press, a delicate balance between ink and water allows this to happen.
Only because of this law of chemistry (i.e., the fact that ink and water repel each another) can a commercial printing supplier use printing plates on which the image area and non-image area are both on the same level. (That is, they are neither raised above the surface of the plate, as in relief printing processes such as letterpress, nor recessed below the surface of the plate, as in fine arts intaglio printing.) And only because of the oily nature of offset lithographic printing ink does this process work.