Depending on the project this process can involve a few layers to achieve a simple hand rendered look of a line and wash illustration. More complicated illustrations can have many more, the line art can be on several layers and composited together from a foreground to background object or character. Colour added to each layer on a separate layer the line art on a multiplying layer setting so that the colour can be seen below. Textures and lighting added each to different layers to achieve depth, atmosphere and enhance any action in the scene.
It can sound complicated and I hope I did not make it sound like goobledygook! Practice and experience in pushing your skills and solving problems on the way will gives you the skills in confidently creating a layered illustration.
As a freelance illustrator with experience in creating book cover artwork, children’s book and picture book illustrations I create each artwork with the brief, story and finished product in mind. I’ve built up confidence in using layers to create the illustration, my top tip is to keep a master copy with layers to be able to edit or grab elements or characters to use elsewhere in the book. The back cover springs to mind as a place wherea ‘drop in’ works well as it always needs a little illustration to sit with the blurb. Building up the artwork in this way, having the experience in understanding how a book is promoted, the print process and digital release makes you a more valuable resource to the publisher/author. Having their confidence in your skills and professionalism as an illustrator will create further opportunity to collaborate with them again.