Gems & Jewelry

You cut, set, cast, repair, and sell stones — this page is your bench reference. The rules for what you can honestly claim about a stone or a piece. Thirty-eight stones with the numbers you read off your own instruments, and the cheapest test that tells each one from what it gets mistaken for. And bench craft from people who do the work, labeled plainly as collected notes until it’s been judged.

Look through the refractometer

This is the view through the eyepiece of the tester on your bench. Pick a stone from the list beside the port and its shadow edge falls where it falls on the scale — and everything about that stone opens up under the meter: its numbers, what to do with it, and the test that tells it apart. A drop of contact liquid (RI 1.81) sits between the stone and the hemicylinder — it is what sets this meter’s top end, so anything reading above 1.81 gives you no edge at all. Choose a different stone and the reading and the record change with it. If your stone is doubly refractive, there are two edges — rotate the polarizing filter and watch the second one come and go. And turn the stone itself, the way you do on the glass: on some stones the edges travel when you turn it. On others, the edge staying put is the answer.

Polarizing filter — rotate it

90°

Slide to rotate the filter. On a doubly refractive stone the second edge is hidden at 0°, strongest at 90°, and gone again at 180°. On a singly refractive stone the one edge never moves.

Stone — turn it, or move to another facet

0°

Turning a doubly refractive stone on the glass moves its edges inside its range — read at a few turns and note the extremes. A singly refractive stone’s edge won’t budge, and that tells you something too.

From the Mine — Digging Deeper

The science on the meter, and the story behind the stone — in one place.

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          RI —
          Birefringence —
          SG —
          Mohs —
        

With this stone, do this

The test that tells it apart

Facts worth repeating

Ultraviolet lamp

Read fluorescence in the dark, against black — on a white ground a faint glow washes out and can be missed entirely. The window going black under the lamp is deliberate.

Spectroscope

Dichroscope

What the numbers mean

Every term the port and the stone records use, in plain words — keep this beside you at the bench.

RI — refractive index: How much the stone bends light; the number the meter reads.
SG — specific gravity: How heavy the stone is for its size, weighed against the same volume of water.
Birefringence: The gap between a doubly refractive stone’s two readings; the distance between its two edges on the meter.
Singly refractive: One reading, one edge, however you turn the stone or the filter (garnet, spinel, diamond).
Doubly refractive: Two readings; the second edge comes and goes as you rotate the filter or turn the stone.
Hardness: The Mohs scale, 1 (talc) to 10 (diamond); what will scratch it and what it will scratch.
Over the limit: A reading past 1.81, beyond what the meter (and its fluid) can show; the stone needs another test.
Spot reading: The approximate distant-vision reading used when a stone can’t give a crisp edge — an unpolished back, a tiny or mounted stone, an aggregate whose edge is diffuse by nature, or a doublet: an assembled stone whose back is only backing material, so the reading has to come off its dome. For a solid stone it is a fallback method: the approximation belongs to the method, not to the stone’s cut. On a doublet’s dome it is not a fallback — a dome makes no flat contact, so the spot is the method that fits it.
Spectroscope: Breaks a stone’s light into a spectrum; elements in the stone swallow set wavelengths, and the dark lines and bands they leave are a fingerprint you read against the scale.
Dichroscope: Two windows side by side, each showing light vibrating one way through the stone — if the colours differ window to window, the stone splits light, and the pair is a name-level clue.
Pleochroism: The colour change itself: two colours in a doubly refractive stone (dichroism), three in some (trichroism), none in a singly refractive one however you turn it.

Start where your work starts

Selling a stone or a piece? Start with the Rulebook. It tells you what words you can use — natural, flawless, handmade, total weight — and what you have to disclose before the sale, in plain words with the section number attached.

Got a stone you can’t name? Put it on the refractometer above, weigh it on the balance, and work the list. Every stone carries its RI, SG, and hardness, plus the cheapest test that separates it from the stone it gets confused with.

At the bench? The Bench collects craft in seven areas — setup, soldering, setting, casting, repair discipline, finishing, safety. Read the label on every card: those are collected notes, not yet judged, so lean on them accordingly.

One standard runs through all of it: a stone’s name is only as good as the tests behind it. Where a number rests on a single source, you’ll see it flagged right on the stone — never smoothed over.

10 rule groups

Complete. All 29 sections of 16 CFR Part 23, grouped into 10 plain-words groups you can search the way you’d ask the question.

38 stones

With their bench numbers. RI, SG, and hardness for each, cross-checked against published gemological references — and flagged on the stone where a number rests on one source.

63 bench notes

Collected, not yet judged. Gathered bench knowledge across seven areas. Useful today; settled only after it’s been corroborated or judged.

The Rulebook

You’re writing a listing, a tag, or a repair ticket — these are the rules for the words you put on it. The FTC Jewelry Guides, Guides for the Jewelry, Precious Metals, and Pewter Industries, 16 CFR Part 23 (2018 revision, 83 FR 40667), are the FTC’s reading of Section 5 of the FTC Act: they don’t bind you by themselves, but the FTC can enforce Section 5 against claims that run against them (§ 23.0(d)). Plain words first, the section citation on every rule, and the Guides’ own words quoted under it.

The Bench

Your craft, in seven areas — 63 notes collected from practitioner forums, trade publications, insurers to the trade, and tool and material makers. Use them the way you’d use another bench’s advice: good working knowledge, worth hearing. But read the label on every card — these are collected bench notes, not yet judged. Nothing here is settled knowledge until it’s been corroborated or judged, and the label stays on until then.

Still to Come

More of your trade is on its way. None of this is here yet — each piece says plainly where it stands.

Mining & Land

Mining claims, public-land collecting rules, and state rules — the far end of your trade, where the stone starts. Notes for it are gathered into a holding file as they surface in bench work, each with its source; the first one logged covers mail-in repair transit practice, from the trade chain.

Held — in the holding file

A Claims Checker

Paste your listing or ad description and have it checked against the rulebook — treatment triggers, naming rules, “natural,” weight claims — with the section citation for each flag. Until it exists, the rulebook above is where you check a claim yourself.

Not built yet

Forum Rooms & Judging

Rooms where you’d talk shop with other bench jewelers and stone people: The Bench, Stone Identification, Honest Selling, Repairs & Restoration. And judging is how the bench notes above stop being “collected” and start being settled — that work hasn’t happened for this trade yet.

Not built yet