. Decal Medium 6 Pack of 17ml Bottles from Vallejo. It improves the adherence of the decal and prevents the formation of air bubbles. It also acts as a cleaner and helps prepare the surface of the model before applying the decal. Before placing the decal, first apply Decal Medium with a brush on the surface of the model and then slide de decal from the paper to the surface; next apply Decal Medium over the decal and press down lightly with a finger or humid cloth to eliminate excess liquid. Decal Medium contains alcohol, and is therefore flammable, but it is neither toxic nor irritating.