When I used to photograph jewellery for catalogues I used a thick mirror positioned so it reflected the unlit ceiling, I then built a custom reflector tent for giving the needed reflections in the product. ( often a simple card tube.)
Using a mirror increases the area of reflectance as it shows on the underside as well... the object is lit as if it is in the middle of a long tube. The black background is simply a reflection of an unlit or partially lit area above. This gives far more options and control than a black plastic base. It was especially effective on small jewellery pearls and watches. I can not count the number of Items I shot this way ... it was many thousands over a two year period.
The double reflection a mirror produced was usuallyy airbrushed out.