Art Spectrum : Artists' Oil Paint : 40ml : Clear

Art Spectrum Clear Artists’ Oil Paint is formulated as an oil paint, but without coloured pigments. With Art Spectrum Clear Oil Paint, the integrity of each brush stroke is retained, which is not the case with most mediums which tend to level or smooth out brush strokes.

It can also be considered a medium because of the effects it helps create.  It can reduce colours to pale tints without the use of whites or mediums.