METAL 
 (  TO RETURN TO    INSTRUMENT INFO.)  > I’ve used aluminium in these because it’s easy to cut,shape, tune,& scratch designs on.
Many metal items-especially from scrapyards - have a natural voice,though, and (like the xylophones) it’s largely a matter of not killing it off.
The bars and tubes make different notes entirely as a result of how long/thick they are.
The gongs are often tuned by hammering a
bulge in their centres.
You can also tune tubes by cutting slots of different lengths in one end or both.