PT950 vs PLAT: Understanding Platinum Hallmarks

What these stamps mean, how they differ, and what else you'll see on platinum jewelry

You're examining a white metal ring—could be platinum, could be white gold. You find a stamp: "PT950." Or maybe it says "PLAT." Or "950PT." Do these mean the same thing? Does it matter?

Yes and no. They all indicate platinum, but the specifics matter for authentication, especially when dealing with fine jewelry from houses like Cartier, Harry Winston, and Tiffany & Co..

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What PT950 and PLAT Mean

PT950

PT950 indicates:

• PT = Platinum (chemical symbol Pt)
• 950 = 950 parts per thousand pure platinum (95% platinum)

This is the international standard marking format, combining the element symbol with the fineness. PT950 is the most common grade for fine jewelry platinum worldwide.

PLAT

PLAT is simply an abbreviation for "PLATINUM." When stamped alone (without a number), it traditionally indicates platinum content but doesn't specify the exact fineness.

In US legal terms, "PLAT" or "PLATINUM" without qualification must be at least 950 parts per thousand—so in practice, PLAT alone implies the same purity as PT950.

Are They the Same?

Functionally, yes. Both indicate high-purity platinum suitable for fine jewelry. PT950 is more precise; PLAT is more traditional. Neither is "better"—they're simply different marking conventions.

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Purity Levels: What the Numbers Mean

Platinum jewelry appears in several grades:

Mark	Platinum Content	Common Name
PT999 or 999PT	99.9%	Pure Platinum
PT950 or 950PT	95%	Standard Fine Jewelry
PT900 or 900PT	90%	Slightly lower purity
PT850 or 850PT	85%	Minimum for "Platinum" (US)
10% Plat	10% platinum	Platinum alloy (not solid)

Why 950?

PT950 dominates fine jewelry because:

• 95% platinum provides excellent durability
• The 5% alloy (usually iridium, ruthenium, or cobalt) improves workability
• High enough purity to call it "platinum" anywhere
• Standard across luxury houses globally

Lower Purities

PT900 and PT850 appear occasionally:

• Some vintage pieces used 90% platinum
• Certain Asian markets favor 900 platinum
• 850 is the legal minimum in the US for "platinum" labeling

For significant jewelry from major houses, expect PT950 or its equivalent.

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When Each Marking Is Used

PT950 (and Variations)

Used predominantly by:

• European manufacturers (precision marking standard)
• International brands operating globally
• Modern production (last 30+ years especially)

Variations you'll see:

• PT950 (no space)
• Pt950 (lowercase t)
• 950PT (number first)
• 950 PLAT (number with PLAT)

PLAT and PLATINUM

Used traditionally by:

• American manufacturers (longstanding convention)
• Tiffany & Co. often uses "PLAT"
• Vintage American jewelry (pre-1960s especially)

These marks reflect US hallmarking traditions, where word marks were more common than numeric fineness stamps.

Regional Preferences

United States: PLAT, PLATINUM, or PT950 United Kingdom: 950, PT950 (with assay marks) France: Dog's head symbol for platinum (see below) Germany: PT950, Pt950 Japan: Pt950, 950

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Other Platinum Marks to Know

Iridium-Platinum (IRID PLAT, IRIDPLAT)

Vintage American pieces often show IRIDPLAT or 10% IRID PLAT, indicating:

• Platinum alloyed with iridium
• Very hard, excellent for delicate work
• Common in Art Deco and Edwardian jewelry

This is legitimate and often indicates quality vintage work—iridium-platinum was prized for its hardness.

French Platinum Marks

France uses the dog's head (tête de chien) to mark platinum, just as the eagle head marks gold. On French platinum jewelry from Cartier Paris or Van Cleef & Arpels, look for:

• Dog's head profile
• PT950 or 950 fineness mark
• Maker's lozenge

UK Platinum Marks

British platinum carries:

• Orb symbol (introduced 1975)
• Fineness mark (950, 999, etc.)
• Assay office mark
• Sponsor's mark

The combination definitively identifies UK-assayed platinum.

Palladium Marks

Don't confuse platinum with palladium:

• PD or PALL = Palladium
• 500 or 950 fineness
• Similar appearance but different metal

Palladium is lighter than platinum—weight is a key distinguishing factor.

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Authentication Applications

What These Marks Tell You

1. Metal identity: Confirmed platinum, not white gold
2. Purity level: Specific platinum content
3. Manufacturing context: Regional/temporal clues

What They Don't Tell You

1. Brand authenticity: A real PT950 stamp doesn't prove a "Cartier" signature is genuine
2. Complete originality: The shank could be replaced
3. Stone authenticity: Metal marks say nothing about gems

Combining Mark Analysis

When authenticating platinum jewelry:

1. Verify the platinum mark matches expectations for the piece
2. Cross-reference with brand-specific marking conventions
3. Check that all marks show consistent wear
4. Consider whether marks are period-appropriate

Example: A Harry Winston piece should show platinum marks consistent with their production era and workshop location. Mid-century Winston pieces typically show American-style PLAT or PLATINUM marks; modern pieces may show PT950.

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Practical Identification Tips

Visual Differences: Platinum vs. White Gold

Before even finding marks, observe:

Property	Platinum	White Gold
Color	Gray-white, slightly duller	Bright white (if rhodium plated)
Weight	Noticeably heavier	Lighter
Wear	Displaces but doesn't thin	Can wear away
Magnetism	Non-magnetic	Non-magnetic

Finding the Marks

Platinum marks typically appear:

• Inside ring shanks
• On clasp backs
• Near connecting points on chains
• On earring posts or backs

Use a loupe (10x minimum) and good lighting. Platinum marks can be subtle.

Testing When Marks Are Unclear

If marks are worn or absent:

• XRF testing: Non-destructive, definitive
• Specific gravity: Platinum is significantly denser than gold
• Acid testing: Platinum resists acids that affect gold
• Professional assessment: Spectra Fine Jewelry can examine and test

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Brand-Specific Conventions

Cartier

Cartier uses location-dependent marks:

• Paris: French dog's head + maker's lozenge
• New York: PLAT or PT950 + American marks
• London: UK hallmarks when applicable

Harry Winston

Harry Winston historically used:

• PLAT or PLATINUM (American convention)
• PT950 on more recent pieces
• Always with "Winston" or "Harry Winston" signature

Tiffany & Co.

Tiffany typically shows:

• PLAT (traditional)
• PT950 (modern)
• Always with Tiffany & Co. signature and country (e.g., "Tiffany & Co. PT950")

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Common Questions

Is PT950 Better Than PLAT?

No. Same metal, same purity (in practice). PT950 is just more numerically specific.

Can Marks Be Faked?

Yes. Marks alone don't guarantee authenticity. They're one piece of evidence, not conclusive proof. Consider marks alongside construction, design, provenance, and professional assessment.

What If My Piece Says 585 or 750 But Looks Silver?

That's white gold, not platinum:

• 585 = 14K gold
• 750 = 18K gold

White gold is often rhodium-plated to appear bright white, but it's gold alloyed with white metals, not platinum.

What About "Platinaire" or "Platinum Clad"?

These are marketing terms for non-solid-platinum items:

• Platinum over base metal
• Platinum alloy with minimal platinum content
• NOT the same as PT950 or solid PLAT

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Related Guides

Platinum & Silver Hallmarks → Comprehensive guide to white metal marks.

Gold Hallmarks by Country → Understanding gold marking systems worldwide.

Cartier Authentication → Specific guide to Cartier's marking conventions.

Harry Winston Guide → Understanding Winston hallmarks and signatures.

Tiffany & Co. Guide → Tiffany's marking history and authentication.

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Need help identifying platinum marks on a specific piece? Send photos—we're happy to help.