First Sketch and find material to learn to draw bone structures

After doing the sketch, use the layers to do the detail work.

To make the color I use the magic wand on the line layer then I invert the selection so that it selects the image inside and in the color layer I make a gray base, in this way I lock the layer in transparency to be able to paint my portrait

After making the color base, I use a background in another layer, to make the shadows I use a separate layer, where I put it in multiply mode, using the polygonal lasso or the normal lasso, we do the shadows with the gradient tool, from the same way I add a layer of lighting using the loop I repeat the operation to apply the lights

by having the layers separately we have the option of making two versions of our drawing