I used Quixel Suits 2 for this.
In gimp take the normal map and de saturate it.
Then invert it.
Then you will need to clamp the range using the levels tools to make the edges a fine as possible.
Bring in your diffuse texture and place it under the above layer.
De saturate that and adjust the brightness and contrast to represent light bouncing off corners. You will nee to hide the normal layer to work on this layer. Remember the whiter the more it shines.
You can add a little grunge to this by using some of the brushes and darkening or brightening scratches and wear.
Turn on the normal layer and then choose screen in the blend section and then using the transparency slider, bring it down so that the two layer blend representing the best of the specular and the gloss of the intended objects material.
Flatten the layers and export as your _s map.
Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz, 2400 Mhz, 4 Core(s), 4 Logical Processor(s), 8gb RAM, Nvidia gtx660, Windows 7 Pro 64bit
