What to do with a coin you can't identify

You’ve dug a coin. You can’t identify it. Maybe the legend is gone, maybe the type is unfamiliar, maybe it’s encrusted with two centuries of mud. The temptation is to do something — scrub it, soak it, photograph it badly — anything to make progress. Resist. Here’s the workflow that gives you the best chance of an attribution without damaging the coin.

Step 1: rinse, don’t clean

Field mud washes off under cold water with a soft finger rub. That is the entire approved cleaning protocol for a mystery find. Pat dry with kitchen roll. Do not use:

• Brushes, especially brass ones — instant permanent damage to surface patina.
• Chemical cleaners, including lemon juice and vinegar — strips silver and copper alike.
• Ultrasonic cleaners— can shatter embrittled silver and dislodge surface detail.
• Tin foil tricks— the chemistry works but it strips diagnostic patina at the same time.

Step 2: measure

Module and weight are diagnostic to a degree most detectorists underestimate. Measurements you should always record:

• Diameterin mm, taken at the widest point. A cheap pair of digital callipers is the right tool; a ruler will do if you’re patient.
• Weight in grams to 0.01 g, on a jewellery scale. The cheap pocket scales sold for coin enthusiasts cost less than ten pounds and pay for themselves immediately.
• Thicknessat the centre — less commonly decisive, but useful for distinguishing some Roman denominations.
• Material— silver, copper-alloy, gold, lead, mixed? A magnet test will confirm iron contamination but tells you nothing about the metal proper.

Step 3: photograph

Photograph obverse and reverse separately, then ideally an edge shot too. Even diffuse light is more important than camera quality — an iPhone in window light beats a DSLR under a ceiling spotlight every time. Full setup details in how to photograph a find for accurate identification.

Step 4: triage by fabric, module, reverse

Before reaching for class numbers, narrow the period:

1. Fabric. Bright silver, debased silver, copper-alloy, gold, lead? See dating hammered silver from fabric alone.
2. Module + weight→ ballpark denomination.
3. Reverse design. Short cross, long cross (voided / solid), quartered shield, Roman reverse type? The reverse pattern alone places ~90% of UK coin finds inside a 100-year window.
4. Obverse portrait. Male / female, facing / profile / no portrait, bearded / clean-shaven?

Step 5: search PAS for similar finds

The Portable Antiquities Scheme database at finds.org.uk is searchable by period, type, region and a dozen other facets. For coins, try filtering by “period: Roman”, “period: Medieval” etc. and looking at the image grid. For artefacts, the typology filters (brooch, buckle, strap-end) are excellent.

The PAS image search is genuinely effective for visual matching. Even if you can’t pin the exact attribution, you can usually narrow to a typology in a quarter of an hour.

Step 6: ask DetectID

If you’re still stuck, upload your photo(s) to DetectID. Add the diameter and weight you measured in step 2, plus the find region. We’ll return up to three candidate identifications with a calibrated confidence and a reasoning chain showing exactly how we got there.

We’re particularly strong on the periods UK detectorists actually dig — Roman, Anglo-Saxon, hammered medieval, Tudor, Stuart. We’re honest about uncertainty: if the photo isn’t clear enough we’ll ask for better shots rather than guess.

Step 7: ask a real person

For genuinely difficult finds, nothing beats hands-on examination by someone who’s seen thousands of similar pieces. Your options:

• Your local Finds Liaison Officer. Most FLOs hold finds days and can examine pieces in person. They’re a public-service resource — use them.
• Detector club identification nights. Most local clubs have one or more members with deep experience in specific periods.
• Online forums. UK Detector Net (UKDN), Detectorist’s World on Facebook, and the various period-specific groups. Photographs that meet the standards in step 3 will get serious replies.
• Auction-house specialists(Spink, Noonans, DNW, Baldwin’s). For high-end pieces, they’ll often give informal feedback by email with good photos. Some run drop-in valuation days too.

Step 8: record it

Once you have an attribution — even a tentative one — record the find with PAS. Recording captures the find-spot, the attribution, your measurements and photographs into the national archaeological record. It’s free, takes ten minutes per find, and gives you a permanent reference number that you can quote in any future sale, exhibition or research.

What not to do

• Don’t clean the coin to read the legend. Either the legend is there or it isn’t; cleaning won’t reveal what wear has erased.
• Don’t commit to an attribution you can’t defend.“Broad Edwardian penny” beats a guessed monarch.
• Don’t pierce it for display.A pierced coin loses 50–80% of its market value. Frame it instead.
• Don’t sell it the same day you find it. You’ll undervalue it. Give yourself a week to identify it properly first.
• Don’t toss the apparent rubbish.A fragmentary mount or a corroded copper-alloy disc may turn out to be the most interesting find of your day. Keep everything until you’ve identified everything.