I mix my epoxy then add brass powder or shavings until it gets stiff. Sorry that isn't that precise but thinking about it I probably have 50/50 epoxy and metal. If you put too much powder it seems to lose it's adhesion and can come out. I then 'grout' the hole, slot or whatever I am filling
Sorry, I didnt mean to start this but as we are here
I use epoxy too for the smaller spaces but i also found that clear resin that can be found in "artists suppliers" is good too. it is a two component resin that dries as clear as glass and as strong as the epoxy. I think its the same stuff they use in the kiddies kits to make key rings and paper weights etc?
The trick seems to be not to use much powder or it doesn't polish up too well.
I just went out to the shed:
The resin is called "clear plaster resin". I ordered my "metals" (brass,copper and alu) from a mail order firm called "Tiranti". The link ishttp://www.tiranti.co.uk and you need to follow the links to "casting".