Danger, danger! I don’t know what kinds of faceted stones you intend
to try to polish with Zam, but my advice would be: don’t!
Zam comes in stick form and is usually used dry on muslin or leather
buffs to polish curved-surfaced cabochons of soft material like
turquoise and malachite. It is not intended as an all-purpose polish
and is quite coarse.
If your stones are soft enough to be polished by Zam you can be sure
the facet junctions will be rounded and the stones will be damaged.
I haven’t tried harder materials with it but wouldn’t take the chance
because there is a risk of damage and faceted stones require an
entirely different polishing technique anyway.
Unless you’re willing to invest in an expensive faceting machine,
laps, etc. and spend considerable time learning the craft, my advice
would be to purchase well-polished stones to begin with. Scratches
on faceted stones are a sign of poor workmanship or careless handling
after purchase. If a number of gems are kept together in a stone
paper they will be damaged by rubbing together even if they’re the
same hardness. This is called “parcel damage” and it’s common.
Inspect stones carefully at the time of purchase and store them
individually either in papers or stone jars. Always handle cut
stones gently, preferably with tweezers. Good luck.