By Rocco Clayfield, Founder & Director, GoldPaid Ltd · Published 24 August 2026
What is in the kit
A standard UK gold testing kit contains four small bottles of nitric acid at graduated strengths, one bottle of aqua regia for 22ct and higher, one bottle for silver, a black basalt touchstone the size of a domino, and usually a needle set of known-carat samples. That is the entire toolkit. Every bottle is a liquid acid; the touchstone is inert; the needles are reference samples you scratch alongside the unknown piece for comparison.
- 9ct solution: a mild nitric acid. Anything below 9ct fizzes and darkens within a couple of seconds.
- 14ct solution: stronger nitric acid. 9ct dissolves; 14ct and above hold.
- 18ct solution: stronger again. 14ct fades slowly; 18ct and above hold.
- 22ct solution: aqua regia (nitric plus hydrochloric). Attacks 18ct; 22ct and 24ct hold for a few seconds before the aqua regia eventually wins.
- Silver solution: nitric acid diluted with potassium dichromate. Sterling gives a blood-red result; low silver gives brown; nickel or steel gives green.
How the test actually works
- Rub a discreet part of the piece (an inside band, a clasp back) firmly across the touchstone until you leave a bright metallic streak two or three millimetres wide.
- Place a single drop of the lowest-carat solution beside the streak, not on top of it, and tilt so the drop just contacts the metal line.
- Watch the streak for five to ten seconds. If it dissolves or turns dark and green, the piece is below that carat.
- If it holds, wipe the stone, re-streak, and repeat with the next strength up.
- Stop at the solution that finally attacks the streak. The piece sits between that solution and the previous one.
The needle samples are there so you can run the unknown streak next to a known 9ct or 18ct streak and compare the reactions side by side. That side-by-side comparison is the part that separates a useful reading from a guess.
What acid cannot tell you
- Exact fineness. Acid places a piece in a band. It cannot tell 585 (14ct) from 600, or 750 (18ct) from 760. A refinery is paid on the actual number, not the band.
- Plated over a lower carat. A 22ct wash over a 9ct core will pass the 22ct acid on the surface streak. Cut deeper, and the reaction changes. This is a well-known trap on eastern-Mediterranean chain.
- Heavy plating over base metal. A thick gold-plated chain will read as gold on a shallow streak and as brass on a firmer one. If two rubs give two answers, the piece is plated.
- Hidden solder joints. Rings and chains are often soldered with a carat below the main piece. Acid on the joint reads the solder, not the ring.
- Stone and hollow content. A ring can be 18ct and half air. Acid says nothing about payable weight.
None of this makes the kit useless. It makes the kit a triage tool. See gold-plated versus solid gold, how to tell for the non-acid checks that catch most plated pieces before any liquid comes out of a bottle.
Not sure how any of this applies to your own items? Send a photo on WhatsApp and ask. We answer honestly, there is no obligation, and nothing is posted until you decide. Or call 07944 014111, 8am to 9pm, 7 days a week.
Safety, plainly
- Nitrile gloves. Not latex, which nitric acid rots through.
- Wraparound safety goggles. A single splash is enough for a hospital visit.
- Ventilated space. Open window, or better, outdoors. Do not test over a kitchen worktop where food is prepared.
- Baking soda solution in a bowl beside you. Neutralises spills and drips.
- Store the bottles upright in the plastic tray they came in, out of reach of children, out of sunlight, capped tight. Nitric acid degrades plastic slowly; check the caps every few months.
- Dispose of used droppers and paper towels in a sealed bag. Do not tip acid down the sink.
Is it legal to own?
Yes. Small hobby quantities of nitric acid at the concentrations sold in gold testing kits are lawful to buy and own in the UK. What you must not do is test someone else's property without their permission — the test marks the piece, and the mark does not come out. In practical terms that means don't "test" a friend's ring across a pub table.
When a home kit is genuinely useful
- Sorting a jumbled tin of jewellery into gold, silver, plated and costume before you commit to posting anything.
- A quick sanity check on a car-boot or house-clearance buy before you pay.
- Teaching yourself the difference between gold and gold-tone. After a dozen tests, the eye gets faster.
- Confirming that an unmarked chain is at least in the gold family, so you know it is worth sending for XRF.
When to skip the kit and just get XRF
Anything you intend to sell should be assayed, not scratched. XRF (X-ray fluorescence) reads the actual composition of the alloy in seconds without cutting, scratching or removing material. It reports fineness as a number (say 587 rather than "somewhere between 14ct and 18ct"), and it does that per item, not averaged across a bag. The full method is on XRF testing explained.
A parcel of a dozen mixed rings tested by acid is a dozen scratches and a rough band each. The same parcel tested by XRF is a dozen exact readings, no damage, and one price sheet you can check. For scrap decisions the second is the one that pays.
Hallmarks help too. If a piece already carries a UK punch of 375, 585, 750 or 916, acid tells you nothing the mark hasn't already said. See how to read a gold hallmark in 60 seconds for the sixty-second version.
What we do at GoldPaid
Every parcel is opened on camera, each item weighed on calibrated scales and tested by in-house XRF. No acid, no scratching, no melting before you have accepted the offer in writing. If you decline, the parcel goes back tracked and free. That is the whole procedure. For the pricing side see how we value gold.
Common questions
Will an acid kit damage my jewellery?
It leaves a small streak on the touchstone and a tiny discoloured mark on the piece where the acid was applied. On a plain band it is usually invisible after polishing; on a decorative or antique piece the mark can be permanent. If the item has any sentimental or resale value, do not acid-test it — XRF is non-destructive.
Can I test 24ct gold with a normal kit?
Only with the 22ct aqua regia solution, and even that eventually attacks 24ct given enough seconds. A four-bottle kit tops out at 22ct. For fine gold, XRF is the sensible route.
Why did my "gold" piece turn green?
Green means the metal reacted strongly with the acid — nickel, copper or brass. The piece is base metal, or heavily plated over base metal.
Can I test a coin with acid?
You should not. A scratch across a sovereign or a Krugerrand destroys the numismatic premium instantly. Coin authentication is done by weight, dimensions, magnet and specific-gravity checks, and XRF on the edge if needed.
Is the silver acid reliable?
Reasonably. Sterling gives a clear red, and low silver gives brown. It cannot separate 800 silver from 925 silver with confidence, and it will not spot silver-plate over nickel unless you scratch through the plating first.
How long do the acid bottles last?
Two to three years if kept capped, cool and out of sunlight. The 9ct and 14ct bottles fade first because they are more dilute. If a solution stops giving a clear reaction on a known reference needle, replace the bottle.
Can I use an acid kit on white gold?
Yes. White gold reacts like yellow gold of the same carat; the rhodium plating on the surface will need scratching through first, or the acid reads the rhodium coat rather than the gold underneath.
Should I acid-test before posting to a gold buyer?
No need. A hallmark reading and a photograph tell any reputable buyer what to expect. The assay on arrival is what settles it. If you want a pre-post opinion, send photos of the hallmarks over WhatsApp on 07944 014111.