Early on, I looked at Rorschach's mask and considered that it was basically an open canvas for adding another layer of storytelling. It creates Rorschach blots, so basically any mirror-image could go there. I was constantly surprised at how Dave Gibbons didn't exploit this to even subliminally create icons in his mask for readers to maybe pick up on...or I'm too dull to have noticed, which is a strong possibility.
My initial thought was to weave in a bit of the apocalyptic into his facial pattern. The character's own existential take on things and the background of a looming nuclear war meant that the obvious choice was some sort of mushroom-cloud pattern. I toyed with these for awhile and had a lot of difficulty making such a shape that both read well if you knew what it was, but could be abstracted out to not be obvious.
These appear in this format, or as a negative image
One day while outside stretching for a run, I noticed something on a neighboring building that I'd seen on many buildings in NYC, but which hadn't occured to me as useful until that moment. During the Cold War, the basements of many residential and other buildings were designated as fallout shelters, and placards were placed on the exterior walls so you knew where you could go hide when the Commies decided to nuke us. Seen now, they are a somewhat amusing reminder of a serious era. I looked at the shape and decided that this could serve a double-purpose: I could create a symbol that was very New York (though I'm guessing the placards were used in other cities, they are ubiquitous here, though I've never noticed them in other cities), which added another layer, and hint at the apocalypse. It had one downside, namely, that it was not a symbol that would be widely understood and it also sorta broke the template of Rorschach's usual blotchy facial patterning. It also had a sorta Jack-o-Lantern vibe about it.
~7x9" Pencil on paper. I've included city names on everything the past few years, and this one proudly bears "NYC" on it.
Digital value study
Upon returning I worked at 11x17", the same size as my Batman, and closer to the comic book cover-format of being tall and skinny. After I printed out my drawing and mounted it on masonite, my wife also reminded me that the brim of the hat didn't seem right--she was continuing to read the book this whole time. Flipping through, she was right--he has a very narrow round brim, so I adjusted that in the paint.
Some folks at DragonCon asked me whether I lay down an underpainting of toned color before I really start. I used to, but in the past few years have replaced that step entirely. What I do when I mount paper to masonite is work on toned Canson paper. This is your garden-variety Canson paper: it is acid-free, non-fading, and comes in a rainbow of colors. I stock a number of colors and choose one that I want to use as my underpainting. I print my drawing on it, prepare the surface to accept oils, and get to work with a nice non-white surface. If you've seen my originals, you'll notice that I leave about 1" around them to account for shipping and the possibility of corner chipping. I use black or white acid-free artist's tape to edge the artwork and help it look a little more crisp before framing. If you were to carefully peel back the tape, you'd see what color Canson paper I used. I rarely let the paper show through--I typically cover the paper entirely with pigment, but the color affects the way the paint sits on it and helps unify the palette. I forget but I think this one was a sort of honey-wheat colored paper to start, a little darker than the windows.
As I painted, the windows were bothering me. They were continuing to operate as big, blank space--too big, too blank. Most cover art needs empty space for type to go over it, and I suppose I envisioned this as a sample to have that space be a high-contrast text box. So at the very last moment I decided to dirty the windows--after all it was an old apartment in a dangerous era for the city. I gave it the look of years of being wiped in the middle of each pane, with the dirt still accumulating around the outside. Then I broke a pane. These lended a good amount of verisimilitude to the piece, as well as helping to break up that space. It was a good instinct. In that era--in real life as well as in the comic--graffiti was everywhere, so I added some. In the lower right you can make out the lines that begin, "Who / Watches/ The /..." and "Watchmen" would fall below the frame--a common tag found in the comic.
All of which resulted in this: