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Identify counterfeit bills

Identify counterfeit bills

Introduction: (Initial Observation)

Whether altering the design of ancient coins or making photocopies of bills with high-tech machines, counterfeiters have made illegal money throughout history.

Merchants on the other hand try to protect themselves by testing and identifying counterfeit bills in every possible way.

I have seen two different methods of identifying counterfeit bills. In banks, I’ve noticed that the cashier always holds the bill under a purple light. At the supermarket, I’ve seen cashiers put check marks on larger bills using a special marker or pen.

But, how do these methods work? How can a bank clerk pass the bill under a purple light and quickly determine if it is a valid bill. What does the marker do?

In this project I will investigate and experiment at least one of the methods of identifying counterfeit bills.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about counterfeit bills and how they may be identified. Read books, magazines or ask professionals who might know in order to find out how a marker or a purple light may help someone to identify a counterfeit bill.

Keep track of where you got your information from.

Visiting a Local Bank:

In a local bank I noticed that the cashier is holding the bills under a purple light to determine if they are real. I asked the bank staff for some information on the method they use to detect counterfeit bills. I wanted to know how it works.

I was told that the purple light is known as UV light. While observing the cashier holding the bills under the UV light, I noticed that nothing is happening and dollar bills are not showing any noticeable change under the light. I asked about that and the response was “Only fake bills will change color under the UV light“.

Later, I tried to find a UV light for myself.

The UV light that I found for use in my experiment was a battery operated long wave UV from MiniScience.com (MiniScience part# UVCLMN). This light also came with a white fluorescent bulb that had no use for me.
I will later make a counterfeit bill and use this UV light to see how does it work. (UV = Ultra Violet)

Visiting a Supermarket:

Most stores test large bills with a special pen. I decided to find out what is this pen and how it works. I visited my local supermarket and asked them about the pen. Cashiers had the pen and knew how to use it, but they had no idea why it works. The store manager buys the pens and makes them available to cashiers.

I decided to do additional research on the Internet. By searching for the word “counterfeit” of phrase “Counterfeit detection” I was able to find many websites. It seems that counterfeit detection is a huge market and there are many competing products for detecting counterfeit bills.

Counterfeit pen also known as counterfeit detector pen is one of those products. This product is available in many different brands and many different size and shapes.Some look like a marker and others look like regular pens

You can find many of these pens by searching for counterfeit pen on the Internet.

Some of these websites had pictures of the pen and instructions on how to use them.

In general if the money is real, pens only leave a light yellow mark; but if the bill is fake, the pen will make a dark brown/blue or black mark.

I could not find a website that describes how these pens actually work and what makes them work the way they do.

I decided to interview a chemist to get more information on this subject.


Interview with a chemist:

The chemist whom I interviewed told me that regular paper contains starch. As a matter of fact, starch is the substance that glues the paper fiber together and gives the paper strength and a smooth surface. Bills are made of high quality long fibers with no starch at all. So any substance that can identify starch, can also identify counterfeit bills.

A well known substance that identifies starch is a solution of iodine. Most likely these pens contain a solution of iodine (iodine tincture).

While searching the Internet, I also saw the following website that provides additional information for identifying counterfeit money.



Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to find out how counterfeit bills are identified.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable (also known as manipulated variable) is money. I will try varieties of dollar bills, foreign bills and fake bills.

Dependent variable (also known as responding variable) is the reaction of the bill to iodine solution.

I will also test the effect of UV light on real and fake bills. In that case the dependent variable will be the effect of UV light on the bill.

Controlled variables are light and temperature.

Constants are test method, tools, and procedures.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

My hypothesis is that paper used in making bills is not available for public and all papers that may possibly be used to make counterfeit bills contain starch and can be identified using a drop of iodine solution.

My hypothesis is based on my gathered information and my observations of counterfeit detection pens.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: Using iodine solution to identify counterfeit bills

Most stores test large bills with a special pen, to see if they are counterfeit. I want to do the same using Iodine tincture. I will test different bills and some fake bills to see how does iodine solution affect the bill.

Material needed:

    • tincture of iodine (Included in Starch Test Science Kit)
    • Samples of different papers
    • a dollar bill (and samples of foreign bills if you have)
    • bread or a cracker

Warning! Iodine is poisonous and will stain skin and clothing. Also, some people are allergic to iodine. Be safe and careful.


    1. Set up all your bills, paper samples and bread on a table.
    2. Use a transfer pipette or a toothpick to put a tiny bit of iodine solution on each sample.
    3. Observe and record the color of iodine solution on each sample. Your results table may look like this:


Test subject Color of a drop of iodine
Dollar Bill Yellow/ brownish
Bread Black
Printer paper


For your experiment results, also answer the following questions.

    • Which papers contain starch?
    • Which papers do not contain starch?
    • Do you think that the papers that do not contain starch can be used to make counterfeit bills?
    • Can you make your own counterfeit detector pen?
    • What foods (other than bread) contain starch? can you test them?
    • What fruits contain starch? can you test them?

Experiment 2: Using UV light to identify counterfeit bills


Some banks and financial institutions who do not want to mark the bills, use UV light for quick detection of counterfeit bills. In this experiment I will test different bills and other papers to see how does UV light affect them.


    • Long wave UV light
    • Samples of bills
    • Samples of other papers or fake bills that might be made using a copy machine.


    1. Set up all your bills and paper samples on a table in a low light room.
    2. Turn on the UV light and hold it about each sample.
    3. Observe any color change or Fluorescence. Record your results in a table.

Your results table may look like this:


Test subject Color change under UV light
US Dollar Bill No change
Other bills …..
Printer paper Bright white
Other papers ……


For your experiment results, also answer the following questions.

    • Which papers change color under UV light?
    • Which papers do not change color under UV light?
    • What other substances or material in your home change color under UV light.

UV = Ultra Violet

Materials and Equipment:

For experiment 1:

    • tincture of iodine
    • Transfer pipette (or dropper)
    • Samples of different papers
    • a dollar bill (and samples of foreign bills if you have)
    • bread or a cracker

Iodine solution and transfer pipettes are included in MiniScience Starch Test Science Kit Part # KITST. They can also be purchased separately from pharmacies and science suppliers.

For experiment 2:

    • Long wave UV light (MiniScience part# UVCLMN)
    • Samples of bills
    • Samples of other papers or fake bills that might be made using a copy machine.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Iodine turns black when it comes in contact with starch. Most paper contain starch and will turn black with iodine.

The special paper used for printing U.S. money does not contain starch, which is one of the ways that you can spot a counterfeit bill.


No calculation is required.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

I am wondering if checks and other valuable documents can be tested the same way.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.