Usually the hamon will be more of a matte finish because of different hardness levels, the polishing compounds used act differently depending on the hardness of the material - and so it leaves a nicely defined boundary.

You have to make it yourself. Man at Arms videos has the processes to make it in their videos.

It depends... traditionally the flattened wafers or tamahagane were folded to rid the steel of impurities. Thusly they only used the tamahagane as their base metal, it being sorted after its carbon content. There are different construction techniques but usually there would be a billet of higher carbon and one of lower carbon steel, those two were then combined via forge welding. I believe you are thinking of modern "damascus" steel, aka pattern welded steel where you take different sorts of steel, which react differently to etchant via for example their nickel content, a mostly visual reason thusly. So no, traditionally folding was done so you could rid the unclean tamahagane impurities, in modern times you layer differernt steels for visual effects in the finished blade. Hope this clears things up.

A ninja sword is just a shorter katana with full size katana fittings. The straight ninja swords you see in movies are a Hollywood invention.

ok didn't know that thanks for the info.

Ha ha. He did