WHAT ARE THEY?
Artist proofs are production Magic cards that were given to artists as a courtesy in recognition of the art they created that is depicted on the card. They are identical to production Magic cards on the front side but are, with few exceptions, white on the back side rather than having the normal Magic card back. Thanks to Jesper Myrfors, Magic's first art director, Wizards of the Coast distributes artist proofs to artists so that they can have examples of their published work for their portfolio and also as an additional form of compensation.
THE FIRST ARTIST PROOFS
Due to limited finances, Wizards did not print artist proofs for alpha, beta, or Arabian Nights. The first artist proofs were printed at the same time as Collectors Edition and have square corners just like Collectors Edition cards. They are known as "beta artist proofs" because the card set is identical to beta. There are no alpha artist proofs, so despite being called "beta" they are in fact the first and only set of artist proofs for the first edition of Magic. (All subsequent artist proofs have the normal rounded corners.) As Jesper Myrfor’s states, “beta proofs and CE cards were printed at the same time, at the end of the Beta run. Call them what you want, but the square corner artist proofs are the first edition of any artist proofs. They were not run as CE proofs, the two were both run off of Beta with a different die cut.”
Wizards distributed 50 copies of each beta artist proof to the artist who created the featured artwork. However, a number of artists, notably Kev Brockschmidt, Richard Thomas and Brian Snoddy, gave away as business cards or destroyed many of the beta artist proofs they were provided. So some particular beta proofs are even more limited in quantity than the 50 that were originally produced.
The only legitimate original source of an artist proof is the artist whose work appears on the card. Most artists sign their artist proofs in order to authenticate that they were acquired from the artist. Some beta artist proofs did not reach the artists, or were subsequently lost or stolen, so autographed proofs are generally considered preferable to unsigned proofs even if the unsigned proof has been authenticated by a third-party grading company.
Some artists gave away a significant percentage of their proofs as business cards, samples of their work, or to friends, and many of these are unsigned. Also, many early collectors preferred to keep their proofs unsigned. So no inference should be make that an unsigned proof is necessarily stolen or inauthentic. Given the very limited quantities of beta artist proofs, and the fact that most unsigned proofs came from the original artist, even unsigned beta artist proofs are in high demand.
An artist proof with a white back is physically not that different from a production Magic card. A bit of connection with the artist can be created when the proof is autographed, but production Magic cards can also be autographed to create that same connection. The unique thing about artist proofs compared to production cards is that the white back provides a blank canvas upon which the artist can create an original work of art.
Many artists will sketch or paint the backs of their artist proofs for a fee, whether you acquire the artist proof from them or purchase it in the secondary market. However, the wait time can range from several months to several years, depending on the artist. And some artists either no longer offer this service or, sadly, are deceased. For these reason, depending on the card, the artist and the quality of the work, a sketch or painting on an artist proof can add many hundreds (or in some cases thousands or tens-of-thousands) of dollars to the value of the card.
AVAILABILITY & PRICING
Several artists still have some of their beta artist proofs available for sale, although the most desirable ones are almost all sold out, and those few still owned by the artist have understandably been priced very high. The majority of beta artist proofs are only available for purchase in the secondary market.
Specific proofs sell rather infrequently and often change hands in private transactions, making it difficult to determine a fair market price. Because of the rarity of these proofs and the difficulty even finding a single copy of a specific one for sale, sellers have a lot of discretion in setting their asking prices. So when you see a proof that you want that appears to be priced at all reasonably, it is advisable to purchase it at that time.
Premiums for painted artist proofs in the secondary market can be significant due to the wait time in commissioning an artist to paint a blank card and the uncertainly as to how such a painting will look.