Counterfeit Detection Guide
How to identify fake Japanese antique coins — knowledge and methods to protect your collection.
Why Counterfeits Are a Real Risk
The Japanese antique coin market contains a significant volume of fake, altered, and problematic coins — a problem that has grown alongside online marketplaces. High-value gold coins and scarce varieties are the most targeted. Once a counterfeit is purchased, resale is nearly impossible and financial loss is virtually guaranteed.
Money paid for a counterfeit is almost never recovered
A single fake undermines the credibility of an entire collection
Unknowingly reselling a fake can make you liable as a seller
Types of Counterfeits
Understanding how coins are faked is the foundation of being able to detect them.
Cast Copy (Mold Replica)
A mold is made from a genuine coin and base metal is poured in. The most common counterfeiting method.
Alteration (Tooling / Re-engraving)
A genuine coin is altered to resemble a rarer date or variety. Date alteration is the most prevalent form.
Cleaning / Artificial Toning
Chemical treatment to improve apparent condition. Not strictly a counterfeit, but severely damages value.
Plated Fake
Base metal core plated with gold or silver to simulate a precious metal coin. Common target: gold and silver coins.
Authentication Tests
Combining multiple tests significantly improves detection accuracy.
Weight Test
EssentialWeigh with a scale accurate to 0.01g. A genuine coin should match documented weight within approximately 1%. Cast copies tend to be lighter.
Dimension Test
EssentialMeasure diameter and thickness with digital calipers. Genuine coins have tight manufacturing tolerances; counterfeits often deviate.
Magnet Test
EssentialGold, silver, and copper are non-magnetic. Any reaction to a strong neodymium magnet strongly suggests an iron-core plated fake.
Visual Inspection (Loupe)
EssentialExamine surface texture, edge condition, and lettering sharpness under a 10x loupe. Compare carefully to documented reference examples.
Acoustic Test (Ring Test)
SupplementalDrop a silver coin onto a hard surface — genuine silver rings with a clear, high-pitched tone. Cast fakes produce a dull thud.
Specific Gravity Test
AdvancedMeasure weight in air and in water to calculate specific gravity. Gold: ~19.3, Silver: ~10.5. Significant deviations indicate plating or base metal.
Counterfeits by Category
Edo Gold Coins (Koban, Oban)
High unit values make these prime targets. Keicho, Kyoho, and Oban koban are especially targeted.
Gold-plated fakes
Silver or copper cores plated with gold. Specific gravity measurement is the most reliable check. Also verify gold fineness using documented specs.
Modern reproductions
Replica coins sold as souvenirs or art objects. Genuine replicas should carry a '写し' (replica) mark — unmarked pieces require extra scrutiny.
Altered mint marks (Gokuin)
The shape and depth of official mint marks (極印) differ by era. Detailed knowledge of period-specific genuine stamps is required.
Holed Coins (Kanei Tsuho, etc.)
Inexpensive in common grades, but rare varieties like mother coins (母銭) command high premiums — and attract fakes.
Mother coin fakes
Common circulation coins are filed down to resemble the crisper mother coins used for casting. Suspicious if characters appear unnaturally thin and sharp, or the square hole is too perfectly aligned.
Script variety fakes
Altering the script style of Kanei Tsuho's 永 character and similar details to mimic scarce varieties. Requires careful comparison to reference material.
Added back characters
Plain-back (無背) coins have mint marks or characters added to the reverse post-production to increase apparent value. Look for inconsistent depth and style.
Modern Coins (Meiji Era and Later)
Machine-made with high precision — check weight and dimensions carefully, plus fine details.
Old 20-Yen Gold Coin fakes
High value makes this a major target. Verify weight (16.67g) and diameter (28.78mm) precisely. Also inspect edge lettering.
Date alteration
Common dates altered to scarce ones. Check closely around the date numerals for removal marks. Compare to auction references for the claimed date.
Trade Dollar (貿易銀) fakes
Heavily counterfeited in China. Key authentication points: 圓 character form, dragon detail quality, and edge reeding consistency.
Authentication Tools
A basic toolkit allows you to conduct your own primary authentication before consulting a professional.
Digital Scale (0.01g accuracy)
EssentialWeight verification is a frontline test for any suspicious coin.
Approx. $15–40
Digital Calipers
EssentialAccurate to 0.01mm. Measure diameter and thickness against documented specifications.
Approx. $12–25
10x Loupe
EssentialSurface and detail inspection. A triplet (three-element) lens minimizes color distortion.
Approx. $8–25
Neodymium Magnet
EssentialMagnetic test for plated fakes. Gold, silver, and copper show no magnetic attraction.
Approx. $4–8
LED Light / Flashlight
RecommendedRaking light reveals surface details, tooling marks, and cleaning evidence.
Approx. $8–18
Specific Gravity Kit
AdvancedWater displacement method for calculating specific gravity. Highly effective for gold and silver coin authentication.
Approx. $25–80
When to Seek Professional Authentication
In these situations, we recommend submitting to NGC, PCGS, or a JNDA-member dealer.
Before purchasing a high-value coin
For coins above approximately ¥100,000 / $700, use only NGC/PCGS-certified coins or have an independent appraisal done first.
Before selling at auction
NGC/PCGS-slabbed coins consistently achieve higher hammer prices. The grading fee is often recovered and more.
For inheritance or estate valuation
Accurate authentication and grading is essential for fair valuation in estate settings.
For unusually scarce or rare coins
The rarer the claimed coin, the greater the incentive to fake it. Treat extraordinary claims with extra scrutiny.
For coins with unknown provenance
If a high-value coin lacks clear ownership history, professional authentication before purchase is prudent.
Major grading services: NGC | PCGS | JNDA (Japan Numismatic Dealers Association)
If You Purchased a Counterfeit
Stay calm and act promptly. The steps below maximize your chance of resolution.
1. Preserve all evidence
Save all correspondence (emails, messages), receipts, and screenshots of the original listing. Document everything immediately.
2. Obtain third-party authentication
Submit the coin to NGC, PCGS, or a JNDA-member dealer for a professional counterfeit determination. A written certificate strengthens your case.
3. Contact the seller
Present the authentication result and formally request a refund. Legitimate dealers will typically comply.
4. Report to the platform
For online auctions or marketplace apps, file a formal complaint through the platform's buyer protection process.
5. Escalate if necessary
If the seller does not cooperate, contact your country's consumer protection agency. In Japan: the Consumer Affairs Agency (188 hotline). Consider filing a police report for amounts warranting it.
6. Record and learn
Document exactly how the fake was identified. The same techniques are reused repeatedly across different sellers.
Fundamental Principles for Avoiding Fakes
Buy from trusted sources — Use JNDA-member dealers and established auction houses with professional vetting.
If the price seems too good, question it — Significant underpricing usually has a reason. The most common reason is that it's not genuine.
Know the specifications — Study the documented weight, diameter, and distinguishing features of any coin you plan to buy.
Handle genuine coins regularly — Museums, exhibitions, and reputable dealers provide opportunities to train your eye on authenticated pieces.
Trust your instincts — If something feels off, pass. This is especially important for high-value purchases.
This guide provides general educational information and does not guarantee detection of every counterfeit. Always seek professional authentication for high-value transactions.