This is a technique that I’ve been experimenting with on my iPad. Using Procreate and an Apple Pencil I start with a basic charcoal sketch over a 50% gray background.

Working with only black or white I refine the light and dark values on a layer set to “hard light”. This means that everything that is darker than 50% gray is multiplied while everything lighter than 50% gray is screened on the layers beneath. Switching to color with an airbrush, I fill in the color values on a layer beneath my hard-light layer.

The values that were painted in grayscale interact with the color to give the final result.

Here is a time lapse video!

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