Artist trading cards (ATCs) are miniature artworks about the same size as modern baseball cards, or 2.5 by 3.5 inches (64 mm × 89 mm), small enough to fit inside standard card-collector pockets, sleeves or sheets. When sold, they are usually referred to as ACEOs (art cards, editions, and originals).
The ACEO movement was started on Ebay by Denver artist Lisa Luree whose Ebay name is bone*diva.
I started making these cards when I was quite ill and confined to bed. When making an ACEO the only requirement is the size. I chose to use watercolor pencils which was an entirely new experience for me. I had always worked in acrylic, but the pencils were portable and and perfect for a bed tray.
Once I thought I might live long enough to see an Ebay auction from start and finish I began participating in ACEO Theme Week on Ebay, and selling these little, easy to mail cards.