The fattest medium. Art Spectrum^® Medium No. 3 is a thicker, more slow-drying medium than Art Spectrum^® Paint Medium No. 2. It is for painters who like a heavier, more viscous, medium. It is ideal for artists who paint in many layers. The artist begins with Art Spectrum^® Medium No. 1, then uses Medium No. 2, then finally Medium No. 3. Art Spectrum^® Medium No. 2 may also be thickened incrementally by adding Art Spectrum^® Medium No. 3 in 10 percent increments.