Certificate · Module 2 of 6

The free Foundation taught you the karat ladder and why a heavier piece can hold less gold. This module starts where that lesson stops — at its own closing section, what purity does not tell you.

The free lesson tells you 22k is 916. This module tells you what the other 8.4% is doing to hardness, colour, castability and resale, and makes you price the consequence.

Where the rounding bites

Three systems describe one idea: karat counts parts of 24, millesimal counts parts of 1,000, percentage counts parts of 100. Only three rungs of the ladder convert exactly.

The two rungs that matter most commercially are both inexact, and they are wrong in opposite directions. 22k rounds down — that is two-thirds of a gram of gold per kilogram traded, given away by the convention. European 14k rounds up, so a European 585 piece is very slightly richer than an American 583 piece carrying the same karat mark.

None of this is fraud, and it is worth being careful about that, because it is exactly the sort of thing that gets turned into a conspiracy video. These are conventions that grew up in different places for different reasons, and every one of them is published. The professional difference is simply knowing which convention you are standing in.

Why alloy at all

A manufacturer choosing an alloy is answering three questions, and only three.

1. How hard does this need to be? This is the honest answer to "why isn't all jewellery pure gold", and most people have never been given it. 24k will not hold a stone and deforms in normal wear. Cost and colour are real secondary reasons; softness is the engineering one.
2. What colour is it meant to be? Copper reddens. Silver pales and greens. Nickel and palladium whiten.
3. Can I cast it? Alloy composition changes flow, shrinkage and porosity in the mould. A design can be impossible in one alloy at a given karat and routine in another.

The buyer inherits the answer — including how the piece behaves when it is resold, which is Module 6.

White gold is not a colour. It is a problem being solved

Gold is yellow. White gold is gold made less yellow by alloying, and then usually made white by plating something else on top of it. Nickel white golds are harder and cheaper; palladium white golds are more workable and dearer. In the EU, nickel is restricted — and note precisely what is restricted:

Then there is rhodium. Jewellery rhodium plating is well under a micron thick and it wears. On a ring worn daily it commonly needs redoing within a couple of years — and this produces the single most common complaint in white gold retail:

"My white gold ring has gone yellow" is not a fault. The ring was always yellowish; the rhodium has worn and the metal underneath is showing. Say that before the sale and you have a customer for life. Say it after and you have an argument — because from where they are standing, you sold them a white ring that turned yellow.

Silver, platinum, and two things people get wrong

Firescale is copper oxide forming below the surface of sterling during heating. Polishing removes the thin clean layer above it and can therefore reveal it rather than remove it. It is a manufacturing defect and a valuer should recognise it on sight.

Tarnish is not corrosion. Tarnish is surface silver sulfide, formed from sulfur in the air. It is superficial, it is removable, and a heavily tarnished spoon has lost no silver at all. This is condition one from Module 1, arriving in practice.

Platinum behaves differently again. It is denser, so the same ring takes more grams. It is harder to work. And it does not wear away the way gold does — under abrasion it displaces rather than sheds, which is why a platinum ring develops a patina instead of getting lighter, while a gold ring genuinely loses weight over decades.

Plated, filled, rolled, vermeil — and a 79× difference

Five terms that sound like variations on a theme. All five have legal definitions in the United States, and they differ by orders of magnitude in how much gold is actually present.

16 CFR Part 23 (FTC Guides for the Jewelry, Precious Metals and Pewter Industries), §§23.3 and 23.4. Last amended 16 August 2018, 83 FR 40667.

Put those definitions on one object. A 10 g flat pendant, roughly 25 × 20 × 1.3 mm, so a surface area of about 11 cm² — an assumption worth stating, because a different shape changes the plated figures and not the filled one.

All three are legal terms with legal definitions, and all three are used loosely by people selling online. When a customer says "it's gold plated", the first honest answer is: which of the five things that phrase can mean?

The resale consequence follows directly. Gold filled has recoverable metal. Vermeil has a silver scrap value and negligible gold — but the sterling base is the load-bearing part of that definition, and it means the object is worth something. Plate on a base-metal core has essentially nothing.

The default karat is a question about the buyer

A 22k buyer and a 14k buyer are not disagreeing about quality. One is buying metal she may need to convert back to money; the other is buying an object he expects to wear every day for thirty years. Sell the wrong one to either and you have failed — and no amount of knowing the ladder will save you if you have not asked which of the two is in front of you.

What this module cannot tell you

It cannot tell you whether the mark on a piece is true. Fineness marking is a claim, and this module has been about what the claims mean. Module 4 is about testing them, and Module 5 is about who is making them and what their word is worth in law.

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Educational content only. Not financial, investment or tax advice. Aurix does not buy, sell, store or broker metal, and does not quote executable prices.