The Power of Gray - The Photoshop: Professional Retouching and Compositing Tips, Tricks, and Techniques - page 101

Here is a smarter way to dodge and burn that uses a 50% gray layer and allows us to work
nondestructively.
1. Open a portrait image in Photoshop ( Figure 2.24 ) , and then go to Layer > New >
Layer. In the New Layer dialog that appears, name the layer dodge & burn .
Choose Soft Light from the Mode menu. Select the Fill with Soft-Light-neutral
color (50% Gray) checkbox ( Figure 2.25 ) and click OK.
Figure 2.24