Most of the lessons in my book, The Realism Challenge, are focused on a single material of some kind: glass, metal, wood, and so on. As you advance in your skills, you may want to take on a realism challenge that includes more than one type of surface. I wanted to try illustrating shiny cellophane packaging, but then I thought, What if I tear it open? That way I could illustrate both the packaging and its contents. So it was that I settled on the image of the candy bars you see here.

1. Not wanting to overload the lesson with too many problems, I decided to tear the packaging in such a way that most of the lettering was removed. The pencil stage is always the time to check and double-check the item for accuracy. I actually took a moment to count the number of "zigzags" in the end pieces of the cellophane packaging. If you're going to do something, why not do it right?

2. The packaging I needed to replicate was a warm, golden color. I decided to begin with a layer of pale yellow watercolor, with the goal of building up the necessary browns and blacks in subsequent stages. As for the chocolate bars, I laid down a fairly dark brown watercolor base, planning to go darker (with colored pencils) and lighter (with white gouache) later on.

3. Here you see me going in with further layers of watercolor. The cellophane packaging provided plenty of high-contrast areas that I knew were crucial for pulling off the shiny effect. Using my fine-tipped brush, I carefully added the different shades of brown watercolor needed in each location, constantly checking the target object for guidance. For the top of the red T, it was enough to get a solid shade of red in place. To achieve this level of opacity, I mixed in only as much water as needed, to make the color move across the page.

4. In this manner, I continued with the watercolors, refining each area of the illustration from top to bottom. The chocolate bars presented a challenge—insofar as the gradient shifts in color were quite subtle. I knew I'd have better luck approximating those subtleties using colored pencil. Still, I took it as far as I could in watercolor, knowing it would look that much better when I switched from one tool to the other.

5. Out came the colored pencils, and I was able to tighten things up throughout the entire illustration. Additions of black in the shaded areas were particularly helpful for making the picture look more three-dimensional. As planned, a dark brown pencil allowed me to give substantially more form and solidity to the chocolate bars. Sometimes your shading process lets you push something back a bit—the silver interior of the cellophane, for example—so that other elements can "pop" a little more.

6. The addition of white gouache made a particularly big difference with this challenge. Cellophane naturally produces loads of white highlights, and even the chocolate had a bit of a pale white shimmer to it. You've got to be careful not to overdo it, though. Add the white gouache highlights only where you see them in the target object. Your goal is always to capture the real world effects of light on surfaces: nothing more, nothing less.

7. THE FINISHED PIECE Part of what makes this challenge interesting is the fact that it presents two contrasting. surface textures. Your eye enjoys comparing the cellophane and the chocolate to see how they differ. Of course, you don't have to stop at just two different items in one realism challenge.

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Reprinted with permission from The Realism Challenge by Mark Crilley, copyright (c) 2015. Published by Watson-Guptill, a division of Penguin Random House, Inc.

Artwork copyright (c) Mark Crilley 2015.