Change the rerolling to have a flux for metal stats and a new flux for gem stats. If you use a metal flux (say silver flux) it keeps the gem stats and only rerolls the metal stats. If you use a gem flux (say topaz flux) it keeps the metal stats and only rerolls the gem stats. Make silver fluxes more abundant since the metal stats on silver aren't worth the money to reroll currently. Add red coral flux, amethyst flux, topaz flux, ruber flux, and adamant flux. This also has the advantage that you can get more granular with the drop rates for things you want more common/less common.