Comment on Space signature tutorial by vnt87

You mean the part about set the blending mode to 'burn' and all? Look on the Layer window, there should be a drop down menu or something where you can select from different blending options (Dodge, Burn, Soft Light, Overlay, Multiply etc.) I havent used GIMP for so long I don't remember exactly but it's in the Layer window. Play with it, you'll figure it out.