Are Counterfeit Pens Always Accurate? No According to the Federal Reserve


Counterfeit pens are commonly used by retailers, casinos, and banks to detect fake currency. These pens are probably more reliable for recently produced currency compared to notes from decades past. Occasionally, there WILL be false positives.

You’ve just found a series 1934D $10 Federal Reserve Note in your cash payment from a customer. The note is worn and not collectible, but naturally you wonder whether or not it is genuine. A quick review of the note’s design and production characteristics seem to indicate a genuine piece of currency. Off you go to the hardware store for a new sawhorse.  As a prolific wood chopper, you’d hate to make a jackass of yourself, fearing you’ll be sent to the mini-porthole where poker chips are hard to come by. 🙂

Turns out Ace isn’t the place to be. The skeptical cashier sees your 1934D $10 FRN and has concerns. Out comes the counterfeit pen. The cashier scribbles all over your note like an angry Kindergartner, and out come the wrong color marks. Ah ha! This is a bum note! He hands it back and you sheepishly give him another $10 note from recent years.

So were you trying to pull a fast one? Not necessarily. The counterfeit pen is NOT infallible.

Have a look at this 1950D $10 Cleveland Star Note, signatures of Granahan-Dillon. Real or fake?

1950D $10 Federal Reserve Star Note - Cleveland - Signatures of Granahan-Dillon - Real or Fake?
1950D $10 Federal Reserve Star Note – Cleveland – Signatures of Granahan-Dillon – Real or Fake?


* Important: A manual inspection with magnifying glass and/or a UV light source (if applicable) is the best way to detect counterfeit notes. Obviously an image on your screen is hard to judge.

A cashier informed a customer this note was fake because of the pen test. We don’t know what brand of pen was used, or what exact color should be produced. Sometimes there are variations based on the pen’s age and type.

For the moment, let’s assume this star note is counterfeit. We’ll also assume the counterfeiter is highly knowledgeable about paper money, so a thorough check is required in spite of the counterfeit pen’s sketchy scribbles.

  1. Yes – Series of 1950D $10 Notes were circulated.
  2. Yes – The signatures are correct – Granahan – Dillon signed this series.
  3. Yes – The older Treasury Seal in Latin is correct for this note.
  4. Yes – The Federal Reserve district of Cleveland circulated notes. All the right numbers and letters are in place.
  5. Yes – The star serial number is formatted correctly, beginning with the letter D and finishing with the *.
  6. Yes – The serial number itself is within the known range reported by Schwartz and Lindquist in Standard Guide to Small-Size Paper Money: 1928 to Date
  7. Yes – The note doesn’t appear to have any errors (legitimate or not) on its obverse.
  8. Not Sure – We can’t feel the paper and engraving work. Passing one’s finger over a lightly circulated piece of USA paper money should produce a “feeling” of raised ink and embossing.
  9. Not Sure – If the note is too circulated to feel the results of the intaglio printing process, is the impression perfectly flat like that of a lithographic press (fake note) or copy machine (fake)?
  10. Need a magnifying glass – Are fibers present in the paper? If so, are they real or merely pen marks or simulations?
  11. Need a magnifying glass – How detailed is the impression? Upon VERY close inspection, does the black ink appear to be printed in dots (a bad note)? Does the impression blur in places where it shouldn’t? Are all the lines and flourishes crisp and sharp, or are they hazy(questionable note)?
  12. No – There aren’t any bank stamps that might suggest it was counted and packed at some point. A legitimate bank stamp would suggest the note is real. The vast majority of notes, however, never get marked at the bank so this isn’t a deal breaker.

Why did the counterfeit pen give a bad test result?

The principle ingredient most counterfeit pen’s chemical makeup is Iodine. Companies also add proprietary chemicals of their own, naturally not public information for good reason.

Pens typically produce no color when they react with genuine United States currency paper. Genuine paper is not bound with starch like normal copy paper or newsprint. Currency is in fact more fabric than actual wood. This allows it to circulate longer before retirement.

One mitigating factor might be the way in which 1950D $10 notes were produced. The Treasury was transitioning from the wet intaglio 18 subject sheet to dry intaglio 32 subject sheet. This could have produced the unwanted side effect of failing counterfeit pen tests attempted decades later. The particular note above could be 100% real depending on the pen’s accuracy on older currency issues.

We think the note is real based on appearances. In reality, a manual inspection is required to be sure. Today’s counterfeit pens might not be reliable for notes produced 40-50 years ago. In fact, the Federal Reserve admits pens are not 100% reliable.

You be the judge and let us know in your comments!

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