Create a parchment layer (or several depending on which tutorial that you follow) and then stick this on top of the layer stack and set the blend mode to multiply...this will make the grays and blacks become dark browns and blacks while the whites will have no influence. Voila, antique map You can then go back and erase the stuff that you don't want (I expect the ocean to come out too dark) and then put a stroke around the landmass, etc.