Oil Paint Mediums & Varnishes

It is not required to use mediums with oil paints. Mediums may however provide desirable properties to the paint, such as consistency, transparency, drying time and much more. 

The paint must be completely dry before you begin to varnish your painting. How long it takes to dry depends on the thickness of the paint application. If you are working with thinner layers, it will dry a lot faster compared to if you work impasto for example, which involves thicker paint application. In general however, drying times will even out due to these pigments very often being mixed on the palette.

The pigment you are painting with is also a factor, as pigments can be quick or slow-drying. Alizarin Crimson or Ivory Black are some examples of slow drying pigments as there is a lot of oil used as part of the paint's binding process. Raw Umber on the other hand contains much less oil content, resulting in a much faster drying process. 

It is always best to check the instructions on the package to mix the medium correctly. However, a great common recipe is to mix one part linseed stand oil with two parts turpentine. You should cover the mix tightly and let it sit for a few days before using it for it to ensure it is completely mix.