I think that mokume-gane (combined metals) blocks could be a good addition.

Mokume-gane (木目金 Mokumegane) is a Japanese metalworking procedure which produces a mixed-metal laminate with distinctive layered patterns, as well as that laminate itself. Mokume gane translates closely to "wood grain metal" or "wood eye metal" and describes the way metal takes on the appearance of natural wood grain. Mokume gane fuses several layers of differently coloured precious metals together to form a sandwich of alloys called a "billet." The billet is then manipulated in such a way that a pattern resembling wood grain emerges over its surface. Numerous ways of working the mokume gane create diverse pattens. Once the metal has been rolled into a sheet or bar, several techniques are used to produce a range of effects.

Mokume-gane would have mixed golden, silver and copper colours, in specific patterns and textures:
Ring patterns, wood patterns, layers, zigzag layers, etc.
Colour combinations of these patterns would be copper-gold, copper-silver, gold-copper, copper-silver-gold, and different gray shades.

To conceive how is this, there are thousands of images about mokume-gane in internet.