About the fish shaped boxes:

Fish and tale is both walnut wood, the tale is ebonized.
Ebonizing wood is a pretty old technique. It has been used to create substitutes for real ebony wood. The classic method for ebonizing is based on a chemical reaction between iron acetate and the natural wood tannins which produces a dark stain.
Iron acetate can be easily made by placing some steel wool in a jar filled with regular vinegar and leaving it there for a few days. When the vinegar solution is brushed onto the wood it reacts with the tannins. The darkness of the resulting colour depends on the tannin content of the wood. Some woods like oak or walnut contain a lot of tannins and will turn fairly dark.
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.Aluminium is a rather light metal and it is quite easy to bend or fold over a mould. I often leave the surface brushed, it gives a cool silky background to the wood.
Or it is given a coat of industrial paint and heat treated afterwards.