The short answer
Skip it. The streak on the tile is metal scraped off your piece, because unglazed porcelain is 6.5 to 7 on the hardness scale and gold is 2.5. A gold streak doesn't prove solid gold either, since a plated piece leaves gold until the plating wears through. A magnet, a scale with a glass of water, or an XRF reading tell you more and leave no mark.
Free: the hallmark chart
Every common gold, silver, and platinum mark on one printable page, with the letters that cancel the number.
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The tip goes like this. Drag your ring across the back of an unglazed tile and look at the line. If it’s gold, the ring is gold. If it’s black, it’s fake.1
I’d skip it, for two reasons.
It scrapes metal off your piece
Geologists use streak plates on rocks, and they file the streak test under destructive tests.2 The plate is 6.5 to 7 on the hardness scale, and gold is 2.5.32 So the gold line on the tile is gold that used to be on your ring.
A gold dealer’s guide says customers who scratched an inherited piece on a ceramic plate “lowered its resale value by hundreds of dollars.”1
A gold streak doesn’t prove gold
The tile only touches the outside. Gold-plated brass leaves a gold line until the plating is gone. A maker of testing kits puts it this way: test the surface of a plated piece and “you will, quite correctly, get a ‘gold’ reading.” That’s why trained testers file a tiny spot first.4
Assayers do use a stone and a streak. They rub reference needles of known karat next to the piece and compare the streaks with acids, and even then the best get within 1 to 2 percent.5 London’s assay office calls that method “an initial indication.”6 A bathroom tile gives you a color and nothing to compare it with.
In November 2025, someone posted a bracelet their dad bought years ago. They’d run it across old china and got “a sparkly yellow streak.” The first reply said it looked plated, with “lots of it” worn off. Their next photo showed the bracelet after a clean with a fine sanding stick.7
Tests that leave no mark
Start with the stamp. Letters after the number, like GF or HGE, mean a thin skin of gold. Then try a strong magnet. If it grabs, the piece isn’t solid gold, and if it doesn’t, keep going, because brass isn’t magnetic either.
A scale and a glass of water catch brass without touching the surface.8 And if real money depends on it, ask a gold buyer for an XRF reading. It’s the X-ray test London’s assay office calls “entirely non-destructive.”6 Some buyers do it free.1
The next step
Run the four stamp checks, then look the mark up in my hallmark chart.
Chapter twelve of my book goes through every kitchen-table test, and which ones to skip. You can read chapter one free.
Sources
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US Gold and Coin, “How to Tell If Gold Is Real: 8 At-Home Tests That Work,” April 30, 2026, usgoldandcoin.com. The same page lists the ceramic scratch test among its eight home tests (gold streak for gold, black or grey for fakes and plating), warns about customers who “lowered its resale value by hundreds of dollars” with it, and offers free in-office XRF. A gold dealer’s guide. ↩ ↩2 ↩3
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Geology.com, “Fool’s Gold and Real Gold,” geology.com/gold/fools-gold. Streak (gold yellow, pyrite greenish black) and hardness (gold 2.5 on the Mohs scale, pyrite 6 to 6.5) are listed under “Destructive Tests.” Gold’s 2.5 is for the native metal; jewelry alloys are harder, and the page gives no figure for them. ↩ ↩2
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Geology.com, “Streak Test for Minerals,” geology.com/minerals/streak-test.shtml: streak is the color of a mineral’s powder; streak plates are unglazed porcelain with “a Mohs hardness of between 6.5 and 7.” ↩
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Quicktest, “Touch-acid testing (and other advanced tests),” quicktest.co.uk, written after the Birmingham Assay Office’s touch-acid training course. Quicktest makes metal-testing kits. The page says to file or scrape the surface “so that you are testing whatever might be underneath,” describes the Assay Office’s three-edged steel scraper, and warns that a touchstone does not remove that step; it adds that XRF “will not usually test through plating.” ↩
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Walo Wälchli, “Touching precious metals,” Gold Bulletin 14, no. 4 (1981): 154-158, doi.org/10.1007/BF03216559. Covers the touchstone method with reference needles and acids, its accuracy (“differences in fineness of 10 to 20 parts per thousand” under optimum conditions), and judging coating thickness from a rubbing long enough “to ensure wear through the coating.” ↩
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Goldsmiths’ Company Assay Office, London, “Our hallmarking methods,” assayofficelondon.co.uk: “the vast majority of assaying is carried out by X-ray Fluorescence Spectroscopy (XRF) which is an entirely non-destructive technique and gives the fineness of the metal in less than 30 seconds. On occasion it may be necessary to remove the surface layer to ascertain the alloy underneath.” Touch testing on a basanite touchstone gives “an initial indication of the fineness.” ↩ ↩2
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“Opinion for piece,” r/Gold, November 9, 2025, reddit.com/comments/1ostx1j. The streak, the dad’s purchase, and the sanding-stick cleaning are the poster’s; the plated-and-worn reading is a commenter’s, from photos. ↩
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Quicktest, “Testing precious metals using specific gravity (relative density),” quicktest.co.uk: “This is a 100% non-destructive test,” while other methods need the metal filed first to get under any plating. ↩