Step 6 Now it’s time to draw some really delicate lines to delineate every part of the body more clearly. For this we’re going back to black-and-white, but this time we will use brushes instead of the Ellipse tool. Select a 9px brush and use the settings shown above.
Step 7 Create a new layer and start brushing with white on every highlight you find important. That done, do the same with black on shadow areas. Create these brushstrokes with an opacity of 100% to get the placement right, then change the opacity to 30% when you’re done. After that, change the layer’s blending mode to Overlay.
Step 8 Select all the layers containing ellipses and brushstrokes. Copy a merged version by hitting Cmd/Ctrl + Shift + C and paste it into a new layer on top of the layer stack. Now duplicate the layer with your stock artwork and put it at the top of the stack. Select this layer and create a clipping mask (Cmd/Ctrl + Alt + G). Change this top layer’s blending mode to Overlay, and its opacity to 50%.