A focal length of between 50 mm and 105 mm is perfect for jewelry photography. If it's wider than this, you simply won't be able to get the best cutout or perspective to frame the pieces. If you overcome this, you'll have too much zoom and won't be able to show any background in your photos. Use a macro lens to capture, for example, all the details of gold or silver jewelry with intricate designs and ornaments.
You can also use a watermark lens to show details in watermarks and publish images in media, such as printing, that require higher image quality and resolution. There are two types of macro lenses for APS-C and full-frame SLR cameras. Choose a focal length of 100 mm or more. The longer the focal length, the more you can keep the camera away from your subject and you'll have a reduced field of view.
Macro lenses allow you to focus more closely on the product than other lenses. The shorter the distance, the better it is to photograph jewelry. The 105 mm macro has a distance of 0.31 m (about a foot). The 18-55 has a minimum distance of 0.28 m.
However, the 105 mm has twice the zoom factor, so the distance of 0.31 m gives you twice as much closeness as the 18-55 mm.