From the manufacturer:
Primary uses for Gamsol:
Thinning oil colors. A little goes a long way; stiff oil colors relax immediately when a little Gamsol is added. Be careful not to thin oil colors too much with solvent alone, this can compromise the ability of the paint to form a paint film.
Modifying painting mediums. Our Galkyd line of painting mediums are formulated with Gamsol, so they readily accept Gamsol as a thinning agent. Note: Gamsol should not be added to painting mediums made with natural resins (dammar, copal, mastic). They require strong solvents such as turpentine.
Studio clean-up: brushes, palettes, palette knives, etc.