My plan was to use the sketch as simply a rough guide for what I would draw in PhotoShop - the original pencil sketch was done rather hastily on a piece of graph paper.
I started doing line art on various layers above the background layer (the scanned image), making sure to use individual layers for the various elements of the graphic: skull eyes, outline, teeth, santa hat and brim, and candy canes. For the eyes and eyes and cheek bones, I simply drew the left eye and cheek, then duplicated them and flipped them horizontally. This allowed me to have a more symmetrical face.
Once I had all the elements inked, I began coloring. I created fill layers beneath the various inked layers that I wanted to color - white for the skull, black for the eyes, red for the hat, etc.
Next up came the shading and highlights. I found a great tutorial at http://www.gomediazine.com/tutorials/a-pseudo-sugar-skull-from-start-to-finish/ which had an excellent tip for shading. I set up my brush tool in a fashion similar to what was listed in the sugar skull tutorial, with brush size varying depending on what I was working with airbrush mode selected, opacity at about 35%, flow at about 35%, and using either near-black or light grey for color. The best part of using the sugar skull technique is that you can create you shadowing layer above the fill layer, then CTRL + CLICK the thumbnail on the fill layer in the layers palette and air-brush away! Your brush strokes will be constrained to within the area selected by CTRL + CLICKING the fill layer's thumbnail. So if you mess up, or you're not happy with the way it's looking, you can simply hit the delete key and start your shading again.
At one point, I had done considerable shading to the skull, but wanted to add more around the eyes, so I simply created a new shading layer; that way I wouldn't have to start over on the entire skull if I wasn't happy with the shading around the eyes.
At another point, I was shading the fuzzy ball on the Santa hat and realized I didn't have the airbrush mode on. I simply deleted and started over. I also found that I had to experiment quite a bit with brush size. If you use a very large brush size, you will tend to get broader, but more subtle results.
I used highlights sparingly - a little on the Merry Christmas banner text, the Santa hat, and skull forehead. Much of my base color was white, so highlights were not necessary, as the shading resulted in highlights in the negative space created by the shading.
For the skull texture, I used a clipping mask to insert a concrete texture photo that I had taken a while back. I've been building up my own collection of textures to use. I often get funny looks when people see me taking close-up photos or brick walls, sidewalks and ceilings. You can see some of my texture photos at flickr.com. I used linear burn and a similar opacity as the sugar-skull example, and I experimented with a couple different textures to find one that I liked.
Below is the finished design, which is available on t-shirts at Zazzle.com. Happy Holidays!
