ACEO is an acronym for Art Cards Editions and Originals. It comes in various materials, including paper, canvas, glass, polymer and metal but the size is always the same: 2.5 x 3.5 inches (6.4 x 8.9 cm) which is the only rule.
People collect them in albums, an ACEO can cost from a dollar to hundreds of dollars. Most artists prefer to sign on the front (somewhere in the corner), but some sign the back and write other details, such as year, email, website, number (for example, 5/50) etc.
If you’re planning on making ACEOs, you can purchase paper you prefer and cut it down to size with a ruler and a scalpel or buy blanks cut to size. Any medium is allowed, from watercolors to markers. When finishing, you can also round the corners if you prefer. Finally, you can ship it to the customer in a plastic sleeve or self-sealing see through bags. These can easily be found online and in hobby stores.
Adding volume is sometimes considered inappropriate as it is harder to store bulky ACEOs, but it is not impossible to add ribbons, buttons, relief paste and similar. Flat ones are more popular and easy to store in albums and sleeves.
Nowadays, ACEO prints are also popular. The process is the same as if with any art print, the only difference is the size so make sure you have a good quality image of your artwork. You may enhance it digitally but keep in mind that it should stay true to the original. Feel free to use a sealer, but include that in the description of the item because some collectors do not like sealed, glossy cards.
For printing, photo paper or giclee is preferred. Keep it acid free and perhaps it’s best to limit the number of prints to emphasize the uniqueness. You may use your home printer, but the best results will be achieved by using professional service provided by specialized companies.
To make ACEOs, you don’t need any expensive equipment. There are a lot of them on the market nowadays so perhaps selling them is not very profitable, but true ACEOS are can also be traded like ATC cards so perhaps try making some inspired by your artwork. It’s fun and very relaxing.