Imprimatura
Imprimatura is a first layer of paint applied onto white background (usually gesso). The paint can be diluted with turpentine or some other solvent to achieve a thin, transparent layer.
Imprimatura serves several purposes:
it helps to seal the porous background to prevent it from absorbing too much pigment from subsequent layers of paint, which might make them look dull;
it allows light falling onto the painting to reflect off the surface below and through the paint layers making colors more vibrant and accurate;
it harmonizes the painting creating a common color “theme”;
it helps with relative color and value matching, which might be difficult on a white surface;
dark imprimatura allows an artist to be more efficient, especially when working on a predominately dark painting.
Initially, I think, artists used imprimatura for tempera paintings to have a unified colored background showing through hatch-like application of the paint bring an artwork together. Besides, a lot of drawings were done on tinted paper, and imprimatura made canvas similar to a familiar drawing surface.
Imprimatura is usually transparent or semi-transparent. Most artists use earth pigments (neutral colors and quick drying time being obvious advantages), but you can use pretty much anything. I tried blue and purple imprimaturas; took forever to dry and the results were questionable, but it was fun.
Here’re some examples from old masters.
The Lion Hunt underpainting by Rubens. He used grey imprimatura.
The Battle of Anghiari (copy of a fresco by Leonardo da Vinci) by Rubens.
Madonna and the Child with Six Angels by Veronese. Technically it’s a drawing (or etching?), but he used the same pearl grey or bluish grey color background for his paintings.
Christ and the Good Thief by Titian. This one has a reddish imprimatura showing through the underpainting.
Holy Family with the Young St. John by Tintoretto. You can see light golden grey imprimatura.
Profile Study of a Bearded Old Man by Van Dyck. The imprimatura is pretty dark (burnt umber?)
