A polished ring is a small spherical mirror. So is a chain, a cabochon and a watch case. Whatever is in the room ends up reflected in the object, which means you are not really lighting the jewellery, you are lighting the room around it. That single idea explains most of what follows, and it is why jewellery shot in an ordinary office looks grey and flat: the piece is faithfully reflecting a ceiling, a window and a photographer in a black jumper.
The basic setup: one hard light, one card, two flags
For the bulk of dealer and valuation work I use one diffused but directional source at roughly 45 degrees from upper left, a white card on the opposite side as fill, and two black cards just outside frame left and right. The white card puts a soft gradient across polished surfaces so metal reads as curved rather than cut out. The black cards are what most people miss: the dark edges on a diamond or the crisp line along a chain link only appear when something black is reflected in the stone. Without black flags a diamond looks like a piece of glass; with them it sparkles. You are not adding light to create sparkle, you are adding the reflection of darkness.
Move the black cards in and out while watching the stone through the camera or a loupe. On a brilliant-cut stone you want the table facet bright and the pavilion returning dark flashes. If the whole stone floods white, the fill card is too close. If it looks lifeless and grey, the flags are too close. Two inches of movement either way is often the difference.
Chains: the two-minute trick
Chains photograph badly lying flat. The links shadow each other and the eye reads a tangled line. Hang the chain over a rod, a stiff wire or the edge of a clear acrylic strip so it falls under its own weight, light it with the same single source, and let the background fall where it will. A heavy curb chain suspended and shot against grey reads as sculpture. The same chain on velvet looks like a printer's error. For catalogue work, one frame of the full chain hanging plus one clasp and hallmark close-up covers the identification requirement, and the hallmark close-up matters for exactly the reasons covered in my article on photographing antiques for insurance.
Colour accuracy decides valuations
Metal colour is a valuation input. Yellow gold, rose gold and high-carat antique gold are different prices, and 18 versus 9 carat reads differently in a warm-lit photograph. Stones are worse: a G colour diamond and a J colour diamond are hundreds of pounds apart, and both look colourless under a tungsten-spiked LED. Use daylight-balanced light, 5000 to 5600K from an honest manufacturer, and set a custom white balance off a grey card placed where the piece sits, not where the camera sits. The card must be in the same light as the object, or you are calibrating to a different light than the one hitting the jewellery.
Check the histogram after the grey-card shot and after every lighting change. A drift of 200K across a session is invisible to the eye and obvious to a valuer comparing your file against a certificate.
Scale, always
A 5 mm sapphire and a 3 mm sapphire are indistinguishable without something to measure against. For insurance and valuation files I include a photographic scale ruler in at least one frame of each piece, and for stock catalogue work where the ruler would cheapen the image, I shoot a second frame with the ruler and file it privately. The client gets the clean image; the file keeps the evidence. When a loss adjuster asks how big the stone was, an approximation costs money.
Depth of field and focus stacking
At macro distances on a 100mm lens, the usable depth of field on a ring is a few millimetres. Stop down to f/11 to f/16 for a single stone in a plain collet, but for anything with height, a three-stone cluster, a Victorian scroll ring, a brooch, focus stacking is the honest answer. Five to nine frames stepped through the subject and blended gives edge-to-edge sharpness that no single aperture will deliver, and stay at f/8 for the stack rather than f/16, because diffraction at f/16 eats the crispness you stacked for in the first place. Focus peaking or a focusing rail makes the stepping repeatable; handheld stacks on jewellery do not survive scrutiny at 100 percent.
Backgrounds and retouching limits
Mid-grey or pale neutral backgrounds flatter both gold and silver and keep reflections manageable. Pure white is hard on jewellery because the reflection of white in metal erases the edges. Whatever background you use, retouch the dust, not the object: a speck on the backdrop is fair game, but a facet that has been cleaned up, a stone brightened, a scratch on a shank removed, turns a record into an illustration. For valuation and insurance work no retouching of the object is acceptable at all. For sales catalogue work, keep it to removing the occasional dust mote and levelling, and disclose heavier work to the client. My working rules on what may and may not be altered come from the same place as the licensing position described in the copyright and licensing article.
What a phone can and cannot do
A modern phone will make a competent record of a ring for a household inventory: dark room, one window, white paper as fill, tap to expose on the stone, and do not use the flash. What it will not do is controlled reflections, accurate colour without a grey card, or the depth of field discipline that stacked macro work gives. For a dealer's stock file, a valuation file, or anything that will be argued over, the controlled setup earns its fee. Commissioning terms are on the services page and current day rates are on the prices page.
One last habit worth forming: shoot every piece twice, once for the client's use and once as an untouched original, filed by date. The second set costs nothing at the time of shooting and is the only thing that answers the question of whether a mark was always there, two years later.