Tom Dixon, age 9, of Camden, N.J., for his question:
According to the Treasury Department's Bureau of Engraving and Printing, a $1 bill will wear out after it has been in circulation for about 18 months. The department also reports that bills of higher denominations last much longer because they do not receive as much handling while in circulation as do the dollar bills.
To make the paper money last as long as it does, the government must arrange for special paper and ink that is made by a secret process. If you look at a new bill with a magnifying glass, you'll see the paper contains tiny red and blue threads not found in ordinary paper.
The job of printing new paper money starts with the preparation of engravings that are used to make the printing plates. After artists draw the designs and the secretary of the Treasury approves the finished product, skillful engravers cut the artwork into steel plates.
One engraver might work on the portrait, another will add the lettering while still other engravers complete the rest of the bill's design. The engraving is usually a team effort.
A completed engraving then goes to a transfer press. This is a machine that squeezes the engraving against a steel roller and presses the design into the roller's surface. In a similar way, the roller will later press the design onto hundreds of printing plates that will be used to print the bills.
High speed rotary printing presses are then used to make the paper currency. The large presses print sheets of 32 bills. The presses include an automatic sheet feeding device that my hold 10,000 sheets in one loading.
The formulas for the special paper and ink are carefully guarded by the Bureau of Engraving to prevent anyone from using them to make counterfeit money.
The design of the bills gets printed first and then a second printing operation adds the serial number, seal and signatures of the secretary of the Treasury and the Treasurer.
After the sheets of currency have been printed, they are cut in half, inspected and finally cut into separate bills. The approved bills are then banded and wrapped for delivery to banks of the Federal Reserve System.
After paper money is worn out, banks withdraw it from circulation and ship it to their Federal Reserve banks. The Federal Reserve banks destroy unfit currency and replace it with new bills.
Look on the face of a dollar bill. The seal and letter on the left side of the bill identify the Federal Reserve district where the bill was issued. The seal on the right side is that of the Treasury.
There are two printing plate identification numbers on the face of the bill. You'll find one on the right, near the bottom, and one on the left, near the top. Printed four times on the face is the number of the Federal Reserve district where the bill was issued.
A serial number is printed twice: near the top on the right and near the bottom on the left.
To the right of the portrait on the bottom is the year in which the bill was designed.