UV light being used to authenticate currency
Some objects glow in ultra violet light because of the phosphors they contain which absorb radiation and emit it as visible light. Many household items glow in the dark, such as detergent, baby powder, tonic water, milk and glue. New $20 bills, certain rocks, minerals and gems also glow in UV light.
Household Items
Black light emphasizes "bluing agents" and makes detergent glow white in the dark
Most laundry detergents contain phosphors that are advertised as "bluing agents." Black light emphasizes these phosphors and makes detergent glow white in the dark. It is detergent that makes white shirts and blouses glow brightly in UV light. You can make your Halloween and party decorations glow in UV light by mixing a mixture of diluted detergent and spraying it on your decorations. Household glue also glows in UV light and is available in basic colors. Most tubes and containers of glue have a small tip which is handy for making fluorescent lettering. The quinine content of tonic water makes it glow blue. Cat urine under black light will glow greenish-yellow. You can buy phosphorescent or UV reactive powders, but baby powder will also glow in the dark. You can add it to candles, paint and even nail polish for your parties, or sprinkle it on your hair. Milk glows a pale orange in UV light. Ripening bananas glow blue. This luminescence in ripe bananas comes from the chlorophyll catabolites accumulating in the banana peels.
New $20 Bills
Newly designed 2003 $20 bill
To make currency more difficult to counterfeit, the U.S. government has issued $20 bills since 2003 with a security thread that will glow under ultraviolet light. Plans are to also introduce this security thread eventually into $50 and $100 bills. If you have bought a black light for your party, you see this thread yourself on your new $20 bills.
Certain Rocks and Minerals
Minerals glowing under black light
Fluorescent rocks and minerals which give off visible light when activated by UV light are popular collector's items. The light given off can be highly colorful and quite different from the normal color of the mineral without UV light. If you wish to collect minerals that fluoresce very differently from their normal appearance, choose minerals such as zippeite, which goes from yellow to a glowing green. Gypsum will go from dirty white to a glowing blue, as will sodalite and fluorite.
Adamite will go from a drab yellow to a glowing bright green. Willemite and calcite with franklinite will look drab white but glow a brilliant green in UV light.
Certain Gems
An appraiser examines a sapphire necklace
Some diamonds fluoresce or glow blue in UV light, while others can glow a variety of colors which are used in identifying diamonds for insurance purposes. UV light is often used to test whether a gem is natural or synthetic. Natural yellow sapphires will glow yellow in black light, but synthetic ones will not glow at all. Natural sapphires without color will shine orange whereas their synthetic counterparts will not shine. Natural emeralds will not glow in UV light, but synthetic emeralds will glow red. Blue sapphires will not glow, but synthetic blue sapphires can glow various colors. A synthetic ruby will glow brighter red than a natural one.
