© Charles Chandler

 

Condensed from: Bob Barber's site.

1. Overlay Mask
   1. Layer → Duplicate
   2. Colors → Invert
   3. Colors → Desaturate
   4. Layer → Add Mask → Grayscale Copy
   5. Layers Dialog → Mode → Overlay
   6. Filters → Blur → Gaussian Blur → 10~30
2. Screen Mask
   1. Select the background layer.
   2. Layer → Duplicate
   3. Move it to the top of the layer stack.
   4. Layer → Add Mask → Grayscale Copy
   5. Colors → Invert
   6. Layers Dialog → Mode → Screen
3. Duplicate the Screen Layer
   1. To increase the effect, just highlight the Screen layer, and duplicate it, multiple times if desired.