I pulled a favour with one of my work mates and he did some elemental analysis of gold dust brushes. Couldnt see any gold?? If it was there it was below the detection limit of the instrument. In fact we were hard pressed seeing any copper as well!! The brush was essentially carbon with silicon. Either the silicon was added in or was part of the binder (glue).
Interesting stuff. So is golddust a trade mark name rather than a description of the content of the product?
cheers
dr fabio