The pattern accentuation is due to oxidation. The different alloys oxidize at different rates when heated. It is best to completely remove this effect if you are going to etch the damascus as the oxides and decarb will make a mess of the etch. If you are just going for topography and want polished damascus, it is still better to etch and then polish, as that decarb will be removed in the cleanup. Ken is correct the damascus contrast is much greater after final heat treatment, but it is not the hardening that does it as much as the tempering of the hardened steel. Fully annealed damascus etches with little contrast, fully hardened steel also etches with little contrast, but hardened and tempered steel "pops". This is due to ultra fine carbides formed by tempering which scatter the light reflected off from the martensite phase that contains them when it is etched.