I agree with the 90mm, but the Canon 50 f/2.5 macro while a sharp lens, I wouldn't suggest. Not only is it handicapped by less than 1:1 magnification, it's design is old and lacks USM. If you're on a budget, the Sigma 50mm offers life size, and only cost slightly more.
However, most smaller lenses in the 50 range have an angle of view of 46 degrees, compared to the 100mm's 23. This can become a problem when trying to isolate subjects while working it tight areas. You'll need a larger background to keep objects behind the subject from being included. Longer lenses also give you slightly more working distance, which is helpful when lighting you subjects.
Otherwise, most macro lenses are all good lenses. If you can afford the extra, Canon's 100 f/2.8 USM macro is an excellent choice between cost, length and build quality having the smoothest bokeh on the market. Otherwise, the Tamron 90 or Sigma 105 should do well in this situation.
Other things to consider if shooting jewelry is a light tent, and/or circular polarizing filter to minimize highlights.
Light tents come in a variety of styles, and prices. As example:
http://www.adorama.com/JTDL90WTK.htmlGood luck, and enjoy.