I would like to know how do you put an amethyst (purple quartz)
to silver, (like etching diamonds)
It sounds like you want the stone to have a 'frosted' look.
If the stone is faceted, all or just some of the facets can be
frosted. If the design is known before the stone is cut, the facets
to be frosted are left unpolished. Just as they were cut with a
4,000 or 8,000 grit lap. The degree of 'frosting' will depend on the
grit of the lap used. A coarser grit will leave a deeper 'frost'.
If the stone is already cut & you want to frost some of the facets,
but not all, The stone can be ground lightly on a coarse (4,000,
8,000) lap . Depending on how you want the facet meets to look when
he stone is done, this 'frosting' can be done free hand or if
accuracy is part of the equation, the stone will have to be doped
& the facets 'frosted' using a faceting machine.
Another way to frost a stone if the entire stone will be frosted is
to place it/them in a tumbler with an appropriate silicon carbide
grit & tumble it/them for a while. The time depends on the grit &
the finish desired. Tumbling will work for both faceted & cabbed
stones. Some rounding of the facet edges will occur if faceted
stones are tumbled.