Christopher Pratt has used lithography as a printmaking medium since the late 1970s, most often in the last decade, as he became more and more concerned with the health risks inherent in the silkscreen printing process. Pratt made his first lithograph in 1978 when he printed Nude by Night Window. He says that he chose lithography for this image because, even though he had never done a lithograph before, he "knew the medium lent itself to night, to darkness, because of its capacity to do rich, inky blacks." He had also never done a print of a figure before, and these two firsts came together in this work. Pratt has made other monochromatic (or single colour) lithographs, including On Water Street - Shadow Stone (1988) and Big Following Sea (1996).
A lithograph is a type of print that is drawn on and printed from a stone (usually limestone) or metal plate. Lithography is based on the idea that oil (in the form of grease) and water repel each other. Like most of his works in other media, Pratt begins his lithography process with a series of graphite sketches, or studies. These studies are generally a progression of images, and often involve a range of options from spontaneous sketches through techniques of geometry. When Pratt is satisfied that a study will lead to what he wants in the final image, he proceeds with the next phase of the lithographic process.
For the actual printing of a lithograph series, Pratt works with a master printer: a person who has had extensive training and experience with lithography, and who helps the artist with the technical aspects of making the print.
To start a lithograph,
Pratt first draws the image on the stone or metal plate with a greasy
material. This can be done in several ways, but is usually accomplished
with a grease or lithographic pencil, or a thick liquid known as tusche.
Whatever the material is, it is always an oil-based substance. Next, the
surface of the plate is treated with a solution so that when it is wet
only the greasy areas will attract ink. The plate is then wetted with
a sponge. Because water and oil (the grease) don't mix, water stays on
the undrawn areas of the image and not the greasy ones.
Next, an oil-based ink is applied to the plate with a roller. Again, because oil and water don't mix, this ink will only stick to the greasy image that the artist has drawn. A sheet of paper is then placed on the printing surface and, using pressure applied by a press, the image is transferred to the paper. If the lithograph is only going to have one colour (a monochromatic lithograph), and assuming that Pratt is happy with the way the image looks, this is the finished print. The print is then editioned and signed and the image is sanded off of the plate so that no further prints can be made from it. This ensures that the print is a limited edition.
Many of the lithographs Pratt has made are colour (or polychromatic) lithographs, such as Fall Sun Setting - Holloway School (1992) and in the mixed media work Above Gander Lake (1997) comprising three lithograph plates printed over a silkscreen 'flat'. This process is much more complicated and can take much longer than a black and white lithograph.