01Decisive
Read 900 PLAT as genuine, not deficient
Platinum-iridium at 900 parts per thousand was the standard American jewellery alloy in the early twentieth century, and the mark discloses it correctly. It is not a modern 950 piece falling short.
PLAT / 950 · Lovenhall Ring
The 900 PLAT & IRIDPLAT Mark
Early twentieth-century American platinum-iridium alloys. Genuine, and often very fine work.
The international marks for platinum, standardised at 950 for unqualified use4 references
American jewellers of the Edwardian and Art Deco periods worked extensively in platinum alloyed with 10 percent iridium, and marked it 900 PLAT, IRIDPLAT or with the percentages spelled out. The alloy is harder and more springy than modern 950, which is precisely why it could be drawn into the fine millegrain and filigree settings that define the period.
These marks are sometimes mistaken for suspect because they are unfamiliar and because 900 is below the modern 950 threshold for unqualified use. They are genuine period marks, correctly disclosing the fineness, and a 900 PLAT Art Deco setting is frequently worth a great deal more than a modern 950 one of the same weight.
Because the value lies in the workmanship and period rather than the metal, condition and originality matter far more here than fineness. Replaced shanks, later stones and re-tipped claws all bear on the price.
References and sizes
900 PLAT · IRIDPLAT · 90% PLAT 10% IRID · PLAT 10% IRID
Establish which of these you are holding before judging it. A genuine piece read against another reference's rules will look wrong when it is not.
Model-specific checks
What decides a 900 PLAT & IRIDPLAT
These apply to this model and not to the rest of PLAT / 950. Work them alongside the maker's general checks, not instead of them.
02Strong
Judge the work, not the fineness
On period platinum the value sits in the millegrain, the filigree, the calibre setting and the originality of the piece. A worn or heavily repaired setting is worth far less than an intact one of the same weight and fineness.
The market
What a 900 PLAT & IRIDPLAT does on the secondary market
Sought after for period Art Deco and Edwardian settings. Value is in the work, not the fineness.
An orientation for honest, unrestored condition — never an appraisal, and never a quotation.
Questions we are asked
- What does IRIDPLAT mean?
- Platinum alloyed with iridium, usually 90 percent platinum and 10 percent iridium, marked on American jewellery of the Edwardian and Art Deco periods. It is genuine platinum work — the iridium made the alloy hard and springy enough for fine millegrain and filigree settings — and such pieces are often worth well above their metal content.
All the PLAT / 950 checks
Free tools of the room
Lovenhall RingRead the whole piece
The mark tells you what the metal claims to be. The instrument reads the setting and the stones together and gives a range to orient you — before anyone charges you for an appraisal.
Free on iPhone & iPad. An estimate, never an appraisal.
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