Re: How do counterfeit money pens work, which detect fake money?

Greetings:

The answer to your question turned out to be quite difficult to track down. 
I’ll explain how I found the awnser to your question so that in the future 
you might use a similar process for finding information.

STEP 1.
First I asked  the people that I work with your question, this usually 
comes up with a solid clue. While most scientists I know are aware about 
the special pens none of them knew how they work. Everyone agreed that the 
checker pens were some  form of chemical indicator; however, what chemicals 
were being tested for on the bills was the question. Chemical indicators 
are usually solutions that test for various chemical compounds and/or 
acidic or base ions by turning various colors. Swimming pool and spa water 
test kits have several different color indicators for testing pH levels 
(acid or base), bromine and chlorine concentrations. 

STEP 2
I then asked the manager at my bank about the pens and he demonstrated a 
pen for me but he did not know how it worked! He also said that the bank 
does not use them because they mess up good bills with marks and they do 
not detect all bad bills! I then wrote down the name of the company on the 
pen.

STEP 3
I then found the company that sold the checker pens to the bank on the web 
and all that their pages indicated was that the pen uses a patented 
chemical to check the paper money. I then also looked up a dozen other Web 
pages for companies selling  similar money checking pens and there were 
several different types of colored or clear checker marking pens for sale 
and while most of them claimed to work on money from many countries, others 
claimed that they did not work on all currencies including Canadian money 
etc. There were a few clues to the process being used on the web pages but 
all said that the chemicals were patented.

STEP 4 (Final step)
I then made a patent search and that turned up several answers to your 
question. Patent searches are an excellent way to find details about how 
something that's patented works; however, it takes a bit of time to find 
the correct titles and patent numbers. You can also make free patent 
searches on the web at the US Patent Office server or the less busy IBM 
patent server URL at: 

http://patent.womplex.ibm.com/. 

Once you find a patent in the topic area that you are interested in each 
patent must also reference similar past patents and you can unravel the 
whole process by checking the references. In general it is best to search 
for the newest patent in a topic area and all previous patents will be 
referenced in the chain of reference patents. I used these key words in my 
patent search: COUNTERFEIT, CURRENCY, and PEN and came up with about a 
dozen patents.

It appears that there are various types of currency checker pens; however, 
they all look for residue chemicals in the paper left over from the paper 
manufacturing process. Starch and iodide salts are the most common compound 
that all the pens look for and some pens claim to also look for other trace 
chemicals. Most, but not all, genuine currencies , use a special 
manufacturing processes that does not leave trace chemicals such as starch 
in the paper..

ANSWER:
Counterfeit  currency checking pens use chemical color indicators to sense 
trace chemicals left in the paper from the manufacturing process. Most  
governments use special paper manufacturing processes that do not leave the 
same trace chemical residues. Starch and iodate salts seem to be the most 
common trace chemical residue tested for in commercial paper.

DETAILS:
The following is a typical pen advertisement at the following URL:

http://www.di-wave.com/lostp/lossp.htm

"With the Counterfeit Money Detector Pen 

TEST MARK ANY AREA OF A BILL. WAIT ONE SECOND
A DARK BROWN OR BLACK MARK MEANS THAT THE BILL IS SUSPECT
A GOLD OR YELLOW MARK MEANS THAT IT IS GOOD.

The yellow mark fades away in a few days. A black mark remains until the 
bill is destroyed. It will detect U.S. Dollars, French Francs, German 
Marks, Japanese Yen, Hong Kong Dollars, Venezuelan Bolivars and Bahamian 
Dollars. 

The pen is approximately the size of a regular fountain pen. No need for 
batteries.100% Guaranteed. standard paper manufacturing.
-----------------------------------------
The following are abstracts from a few of many patents that I found in the 
money checking topic:

Patent Number 5393556
Title: Composition and method for detecting counterfeit  paper currency 

A chemical solution to detect counterfeit paper currency comprising 
metallic iodine of 99.9% purity, and a solvent selected from the groups 
consisting of alcohols, polyalcohols, ketones, esters of the alcohols or 
the polyalcohols, with formic, acetic, propionic or lactic acid, ethers of 
methyl, ethyl, propyl, or butyl alcohols, or of the polyalcohols, mixtures 
of solvents selected from one or more of the groups, the selected solvent 
being not completely soluble in water and being mixed, at a temperature of 
20° C. with distilled water in a volumetric ratio ranging from 99 percent 
to the volume of saturation of the selected solvent with the distilled 
water, at the temperature of 20° C., the metallic iodine dissolved at a 
temperature of 20° C., in the selected solvent. 
-------------------------------------------------
Patent Number   973744
 Title: A security paper authenticating system
 
ABSTRACT:   A security paper authenticating system comprises, in 
combination, a security paper carrying both starch and an iodate salt, 
typically potassium iodate, and an authenticating composition comprising an 
acidic solution of an iodide salt, typically potassium iodide, the system 
being such that on applying the authenticating composition to authentic 
security paper, as by a pen, brush or stamp pad, iodine is generated and a 
characteristic starch-iodine coloration is produced. The authenticating 
composition is preferably aqueous or part-aqueous, and is preferably made 
acidic by means of a weak organic acid such as tartaric acid. The 
authenticating composition preferably also contains an antioxidant such as 
ascorbic acid. The invention extends to the paper and the authenticating 
composition individually. 
-------------------------------------
Patent Number 496349
Title: A method of detecting counterfeit paper currency
                            
ABSTRACT:   A method of detecting counterfeit paper currency includes 
applying a test solution having an initial color to an area of a paper 
currency to be tested. After waiting for a predetermined time period, the 
color of the test area is compared with a predetermined standard to 
determine if a reaction has taken place, whereby on the application of the 
test solution to a counterfeit paper currency the net result will be a 
color change from its initial color to a black coloration and for a genuine 
paper currency there will be no immediate change in its initial color. 
What I claim is: 
    1. A method of determining illegitimate paper currency by detecting the 
starch content therein in excess of the genuine currency, comprising the 
steps of: 
(a) providing a paper currency to be tested; 
(b) providing a test solution including iodine and having an initial color; 
(c) applying said test solution to an area of said paper currency; 
(d) waiting for a predetermined time period; and 
(e) comparing the color of said area of said paper currency with a 
predetermined standard to determine if a reaction has taken place; 
(f) whereby on the application of said test solution to a counterfeit paper 
currency the net result will be a color change from its initial color to a 
black coloration due to the reaction with starch in the counterfeit paper 
currency and for a genuine paper currency there will beno immediate change 
in its initial color. 
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Best regards from your Mad Scientist
Adrian Popa