There is a wonderful technique for etching on wood called “kolrosing” that is often used for replicas of ancient harps and lyres. It consists of cutting a design into the wood with a very fine blade, and then rubbing charcoal and wax into the surface to bring out the pattern. I have never seen it used for a theremin but I think it would be GREAT!
Using blood is a wonderfully romantic idea - and kind of witchy Game Of Thrones - but the results will be disappointing. Anybody see THE RED VIOLIN, where the luthier used the blood of his dead wife to color the varnish he used on his instrument…..
Here is a demonstration of the use of the technique of “kolrosing” on a replica of the Trossingen lyre by luthier Michael J. King.
https://youtu.be/U8WmwVQe3X4