Art trade cards are printed on heavy, cardboard stock. They measure 2.5x3"/6.3x8.7 cm with on the front artwork and on the reverse sketches, studies in b&w and/or commentary by the artist. Each set consists of 90 cards by one artist. You collected these by buying satchells, but these are complete sets.
Usually each set and additional 5 bonus cards in foil. These are listed and sold seperately.