What does a 'greasy substance' do in the lithographic process?

In the lithographic process, a 'greasy substance' plays a crucial role by repelling ink in non-image areas. This principle is rooted in the chemistry of lithography, which is based on the immiscibility of oil and water. The printing surface is prepared so that areas meant to receive ink are treated to attract the greasy (oil-based) ink, while the surrounding areas that are coated with a water-soluble substance repel the ink due to their wet nature.

By ensuring that the non-image areas repel ink effectively, the greasy substance allows for a clean separation between the printed and non-printed surfaces. This leads to high-quality prints with sharp lines and defined images, which is essential for the overall effectiveness of the lithographic printing process. This characteristic is fundamental to the success of lithography as a printmaking technique, allowing for detailed and precise reproduction of images.