Lithography

Post Etch

So we have, then, is carbon dioxide bubbling off and the vegetable oil hydrolyzing to form the fatty acids and glcyerin. Limestone itself is basic and will then react with the fatty acids to form the fatty acid calcium salts at the surface. The point to remember is these fatty acids then become chemically bound to the surface since they take the place of the carbonate lost as carbon dioxide. Even if you wash away the gum arabic (with water which also washes away the glycerin and nitric acid) or wash away the the ink with a solvent (and so removing the drawing), the fatty acid groups are still bound to the surface where you made the drawing.

In fact it is customary to remove the drawing at this point which sends beginning students into mild shock. But you will see that all is not lost. That is you will if you click here.