Its a dodge brush onto a 50% grey layer set to overlay. It's not quite finished yet. It's still a bit rough and needs some work. Here's the xcf (shrunk to 1000x1000 to get under the filesize limits)
If that isn't the bit you need, the image layer that is listed as 'background' in this one is broken out into layers in a separate image file. It was getting a bit hefty so I had to flatten it before carrying on.