black backgrounds have their place but the amount of black framing around the fig in the composition, the focus (a good macro lens coupled with stacked layers in retouching, can help the fuzziness at the edge of depth of field) and last all good 3 point lighting needs a lot of attention to avoid the issues raised. When i send photos of my jewelry to the selection juries of art festivals, i always black or dark backgrounds so that attention always goes to the artwork.