Wilson's Medium is a clear, gel-like oil based on the 18th century oil painting medium of thickened linseed oil, turpentine and beeswax used by the English landscape painter, Richard Wilson (1 August 1714–15 May 1782), who may fairly claim the honor of being 'the father of British landscape painting,' and, according to George Field, also used by Joshua Reynolds. Rublev has taken the original formula and improved upon it by using the palest bodied linseed oil, pure distilled gum spirits of turpentine and rheological castor wax instead of beeswax.

Castor wax is obtained by the controlled hydrogenation of natural castor oil. When molten it is clear, transparent and largely colorless. Castor wax is practically odorless and has the same toxicity as linseed oil or other vegetable oils. Castor wax is extremely hard in comparison with most other waxes, so it can be used in much smaller amounts than beeswax to provide the same properties.