easy way, print a damascus template on vinyl, apply that to a block of aluminum, and paint it on. The swords from Spiderman 3 were done this way (yet with the pattern being sandblasted first) with the rubber swords using the vinyl template applique as the actual damascus pattern. Youll see in the attached photo various color and material tests on a sword blank which were sandblast and paint, just paint, aluminum black, just the template with a clear coat to lock it in place.
Or, if you must have it actual cast in color, sculpt your master base, hand etch the pattern in, use black iron oxide powder, graphite powder and whatever color silver base you prefer (aluminum and then tone it down with the iron oxide/graphite) brushed into the mould.
Lastly you could have a lot of fun with Crayola brand crayons. Melt some silver and black in separate cans, I use cleaned out soup cans on the stove top. You should learn a method within minutes of pouring colors in rotation and angling the mould. Its what material I would use if melted parts had to be done on camera in real time. Crayola crayons specifically due to the wax and color content not separating when melted. Other brands of crayons may work but I stick to what I know works.