The light angle helps, no doubt, but the depth of the ink in this microscope photo of a one dollar bill is impressive. Keep in mind that the dollar bill is only 0.0043 inches thick (o.1 millimeters):
SIZE: US currency bills are are 2.61 inches wide and 6.14 inches long; they are .0043 inches thick and weigh 1 gram.
COMPOSITION: Bills are composed of 25% linen and 75% cotton; red and blue synthetic fibers are distributed throughout the paper.
PRODUCTION OF DOLLAR BILLS: It costs the US government 4.2 cents to produce a U.S. bill. US currency bills are printed by the Bureau of Engraving and Printing (BEP). The BEP prints about 16,650,000 one dollar bills each day. Most of these are used to replace worn, older bills (which are shredded). According to the US Treasury, there are billions of one dollar bills in circulation.
LIFE SPAN: The average dollar bill has a life span of about 18-22 months.