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Before you bring your sketches to life with paint, you will need to transfer them to the appropriate paper. For a simple solution, try photocopying your sketches directly onto watercolor paper using a printer. If your printer is unable to handle heavy watercolor paper, try a traditional charcoal transfer. Rub the back of your sketching paper with charcoal, attach it charcoal-side down to your watercolor paper, and retrace the image. Upon removing the sketch paper, you should be left with a carbon copy of your original sketch on the watercolor paper. Before painting, whip up a quick thumbnail study of your color palette. The colors of a children’s book can contribute as much to the mood and feel of the work as design of the drawings, so make sure to consult with the author concerning the book’s hues. Bright, vibrant colors often convey cheerful emotions, while dark amber and dark blues can give your illustrations a more somber feel. If you are new to painting with watercolors, you may want to produce some extra carbon copies for practice before attempting your final piece. Remember: painting with watercolors takes a lighter touch than other forms of painting. Brush lightly, and practice with multiple drafts to develop your skills. For extra contrast, definition, and pop, add pen outlines to some or all of your lines. To prevent bleeding, try using a pen with waterproof ink.  For a more comic-like feel with harder, firmer edges, try outlining your lines with ink before painting, and simply filling in the lines. Remember: ink is optional! If you are aiming for whimsical, abstract feel, limiting your outlines or leaving them out altogether are both viable options.

Summary:
Transfer your sketches to watercolor paper. Determine your colors. Paint with a watercolor brush. Define your lines with a pen.