Artist John Avon has illustrated a whopping 172 Magic cards. He's justifiably known for his detailed landscapes—including original Mirrodin block artifact lands Seat of the Synod and Darksteel Citadel and all ten Ravnica "bounce lands"—but his full body of Magic work displays an impressive versatility of style, subject, and composition.
The first step of the creation of a card's art is its art description. The art description tells the artist what the card will do, what its flavor is, and what the mood of the illustration should be. Here were the instructions John was given for Mirrorworks (which, unusually, happen to include what would become the card's final name):
Color: None (artifact)
Location: Cavernous, blue-aligned Phyrexian facility in Mirrodin's Phyrexian interior
Action: We see a sinister, complex device inside a Phyrexian lab. The device consists of a multitude of mirrors, each mounted on a mechanical arm. The mirrors all point partially in the direction of a mirrored platform that sits empty. Most of the mirrors are cracked, streaked with dark stuff, or otherwise marred, but this device still hums with arcane power.
Focus: the Phyrexian "mirrorworks"
Mood: An eldritch duplication device in a dim, sinister setting
With that art description to work with, John submitted a sketch to the Magic creative team:
The sketch is pretty stunning, and for a lot of Magic settings, it might have been given a thumbs-up with no changes. But this isn't just any mirror-festooned creepy laboratory; it's a Phyrexian mirror-festooned creepy laboratory. Armed with feedback from the creative team, John reworked the sketch, infusing it with a little more—or a lot more—of Phyrexia's unique brand of technorganic horror:
Oh, yeah. That's the stuff. The vile, twisted, ichor-stained stuff.
With the go-ahead from creative, John produced the final art:
The final art captures both the shining, reflected light evident in the first sketch and the Phyrexianized nastiness of the second—the perfect blend of "Ooh!" and "Eww."
Here's the final card as you'll see it in Mirrodin Besieged booster packs: