Solubility in Lithography

This week in class, we learned about how polarity affects solubility. Difference in solubility is especially valuable in the art of lithography, a kind of print-making developed in the late 18th century. This chemical process was developed by a writer/composer looking for a cheap way to print his work for distribution. I find it particularly interesting this chemistry-intensive medium was invented for artistic purposes, and it has been used by many artists in many variations ever since.  This includes artists here at Wellesley; I am currently taking ArtS219, Intro to Lithography.

When most people think of printing, they think of relief printing, where ink is put onto the raised areas of a carved block and then pressed onto a paper. This is the kind of method used for everything from the Gutenberg press to children’s rubber stamps. However, lithography operates on an entirely different premise. Instead of having raised and lowered areas on the printing surface, there is only a single plane. How does this work? Below is a simplified explanation of how differences in polarity makes lithographic printing happen.

While relief printing differentiates the inked and blank parts of the image through change in height, lithography differentiates those areas chemically. The surface (traditionally limestone) is carefully prepared to absorb both polar and nonpolar substances. When the artist draws on the surface using greasy crayons or ink, the nonpolar grease is absorbed into the surface. Later on, when (polar) water is washed over the surface, it can be absorbed by blank areas but cannot interact with the greasy drawing.

The surface is kept wet during the inking process, so that there are polar areas (covered by water) and nonpolar areas (where grease was absorbed). An oil-based ink is used, so the ink is nonpolar as well. That means that the ink can interact with the nonpolar areas, but will not interact with the polar areas. When the ink is rolled onto the surface, it sits overtop of the nonpolar areas, but refuses to interact with the water and so does not go onto the wet areas. The overall effect is that the drawing has ink applied to it, while the blank (wet) areas remain blank. The resulting, partially-inked surface can be put against paper using a press, which prints the inked image onto a piece of paper.

The above process can be a little difficult to visualize; if you’d like to see lithography in action, take a look at this short video from the Museum of Modern Art.

www.youtube.com/watch?v=G-PFEbQ5UGc