Ultraviolet Light and Black Light: a beginner's guide
by David Rudd Cycleback

1) Introduction

2) What is ultraviolet light?

3) The different kinds of UV light

4) Your tool for this guide: a black light

5) Where does ultraviolet light come from? How was it discovered? Why can't we see it?

6) How are black lights made?

7) Practical and interesting uses for your black light

8) Examining art and collectibles: Introduction

9) Identifying modern fakes of antique paper memorabilia

10) Identifying counterfeit US currency

11) Identifying alterations to art, collectibles

12) Examining cloth

13) Examining art glass

14) Making glow in the dark art and crafts

15) Protecting yourself from the Sun's UV

16) UV light in science and industry

Practical and interesting uses for your black light

This chapter looks at some practical and interesting areas where you can use your black light.


Invisible ink pen and secret messages and security

A useful, fun and inexpensive tool is the invisible ink pen. Looking similar to regular felt tip pens, they write with ink that is invisible in daylight but fluoresces brightly in the dark under UV light.

UV ink pens are widely available online, including at and eBay. Many sellers of black lights sell the pens. You might be able to pick up some UV ink pens when you buy your black light.
People use invisible ink pens for a wide variety of purposes including writing secret notes to friends and, as described in a later chapter, making glow in the dark sketches and art.

Invisible ink is often used to secretly mark objects, including vases, painting, prints and documents for later identification. A family might mark the bottom of valuable heirlooms in case of theft or dispute. You might write you name on the back of a painting. This will aiding to show it was yours in case of loss. If the marking was written in visible in, a thief may simply scratch it off or mark over it. With invisible ink the same thief will have no idea the painting is marked.

An online seller or brick and mortar store of radios parts or dolls may have a problem with customers who return damaged goods they didn't purchase from the seller. If the seller puts an invisible ink mark on the back of the items before sale she can be sure that the customer is returning the original item.




UV ink hand stamps for dance clubs, bars and concerts
You can buy UV ink and ink pads for your rubber hand stamp. These can be used for secret marking like with UV ink pens. Clubs often stamp the hand of patrons with invisible ink. This allows the patron to leave and return, while allowing the club catch those trying to sneak in without paying.

For identification purposes, Major League Baseball put a fluorescent stamp on the ball Barry Bonds hit for his record 73rd home run in 2001.




Judging the authenticity of drivers and other licenses
Most state drivers have markings that are invisible except under backlight. Others cards, including credit cards, often have similar UV fluorescent markings. Black lights are used to help identify forgeries and counterfeits. Alterations to these licenses can often be detected with a black light, as the added paper, glue or other material might stand out from the rest of the license and other untampered with licenses.



Checking the cleanliness of kitchens and bathrooms
Under black light, otherwise invisible stains in sinks, tabletops, bathroom floors and the like can fluoresce under black light. They often fluoresce yellow.

Black lights are sometimes used to check the cleanliness of motel and hotel rooms, public bathrooms and the like.


Testing if Glass Blocks UVA and UVB Light
Glass that blocks both UVA and UVB light is used for protecting art, collectibles, clothing and other items. Sunlight, and even artificial light, can fade paintings, prints, autographs, posters, rugs and other items. UVA and UVB blocking glass is also used to protect humans from damaging sun. Though not a definitive test, you can use your black light as a quick test if glass blocks UVA and UVB light.

Most standard glass, including for windows and art frames, block UVB but not most UVA. Your black light gives off only UVA, and you can assume the glass blocks UVB. To test the glass, you need something that fluoresces very brightly under black light, like white paper or a tennis ball. In the dark, shine the black light at the glass with the fluorescent item on the other side. If the item fluoresces very brightly, the glass blocks the black light. If it doesn't, the glass appears to block both UVB and UVA.

As your black light gives off a specific wavelength, not the whole UVA range, this isn't a complete, laboratory test. However, it still is a fair test. Glass that allows UVA light through will be obvious.


Finding Scorpions in the Dark
Many scorpions fluoresce under black light


Finding rats and mice
As rat and mice urine fluoresces under black light, exterminators and biologists trace the rodents with black light. You will often see the pest exterminator carrying a black light. I've seen two sitcoms where a pest exterminator used a hand held black light, King of the Hill and King of Queens).



Next: Examining art and collectibles: Introduction


(c) david rudd cycleback, all rights reserved