art supplies; art materials
Refers to physical materials used for drawing or painting, such as paints, brushes, canvas, etc.
画材屋で新しい絵の具を買った。
I bought new paints at the art supply store.
この画材は
subject matter of a painting; motif
Refers to the theme or subject depicted in a painting, not the physical materials. Less common than the 'art supplies' sense.
彼の作品の画材は主に風景だ。
The subject matter of his works is mainly landscapes.
These art materials are easy to use even for beginners.
art supply store
Compound of 画 (picture, painting) and 材 (material, subject). The 'art supplies' sense is the most common modern usage.