I'm a long-time comic book reader and collector. I always followed Overstreet Comic Price Guide on my grading of comic book conditions. One major no-no in the comic book collecting grading was any writing on a comic book. It automatically downgraded any comic to a very good/good/poor condition. In the ninties, when getting books signed increased their market value, I did not participate in that craze. I still saw it as degrading the comic. Then I discovered blank cover variants.
Comic book conventions have grown larger and larger, year after year. With that growth the publishers started printing stark white, blank variant covers that artists can sketch on. So rather than just getting a signature, you get a unique work of art from your favorite artist. The old-school comic guy still sees this as ruining a comic's value but the fanboy and artist sees it as collectible artwork and revenue.
The paper quality of these covers varies greatly. So far I really like the DC New 52 and the Marvel Now covers. Anything earlier than that takes extra patience and limits the type of media you can use (Pre-Marvel Now blank covers are just terrible).
I recently stocked up on several issues featuring these blank covers and am having a great time illustrating these for fans and collectors. Here's a link showcasing of some of my favorites.
Pricing for these follows my commission rates. Feel free to contact me (firstname.lastname@example.org) for any requests or follow me on facebook, twitter or instagram as I frequently post artwork in various stages..