Thinners, turpentine, MEK, denatured alcohol, acetone, resins, lacquers, varnishes, stains
Most paints and paint-related solvents are regulated as flammable liquids and are forbidden in carry-on or checked baggage.
Many (but not all) artist paints are nonflammable and, if posing no other hazard, may be carried in carry-on and checked baggage. However, paint not marked nonflammable by the manufacturer could be removed from luggage by airport screeners. If the manufacturer's material safety data sheet (MSDS) indicates the paints are nonflammable, packing the MSDS with the paints may help avoid their removal from baggage.
An MSDS will show if a paint or related product is a flammable liquid or not. When checking the MSDS, a "flash point" at or below 140° F (60° C) indicates it is a flammable liquid and may not be carried in airline baggage.