Kids, do you like using a black light to check for glowing objects? Do you like to solve clues and riddles? Are you curious about how things are made? If you answered yes to all of these questions then you might like this activity. Some antiques, collectibles and memorabilia have value if they're authentic and in good shape. Many people like to go to garage sales, antique shows, or even just "picking", to find interesting and valuable items.
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
It's often very hard to tell if an old object is authentic or fake, or if it's been repaired or touched up. But using a black light can offer some clues. That's because some telltale signs of repair and signs of age will fluoresce under ultraviolet light.
"Black light" is another name for ultraviolet light, that is, light that is of such a short wavelength that it is beyond the violet end of the visible part of the spectrum. As such, our eyes can not see this light or most objects illuminated by this wavelength of light, so it looks "black" to us. However, a number of materials fluoresce when illuminated by this light. That is to say, they absorb light energy in this region of the spectrum, and re-emit the energy at a longer wavelength, which is visible to the human eye. DayGlo® highlighter pens make use of this property by containing dyes that convert the ultraviolet component of sunlight or of some interior lamps to light of the same color as the pen color, to make the pen markings appear extra bright. We will use this ability of some materials to fluoresce when exposed to ultraviolet light to perform our detective work in this month's experiments.
- Detect Ceramic Repairs. Check an old-looking plate, teacup, or figurine in a darkened room. Use a handheld black light to check for repairs. If glue was used to repair cracks or replace chips then it will be obvious under the black light. This is because modern glues fluoresce under ultraviolet light. Modern paints also fluoresce, so you can also see touch-ups and repainting jobs.
- Confirming Age of Paper Items. Old postcards, books, signs, photos, posters etc. made before the late 1930's rarely glow under a black light. But the bleaches and dyes used in modern papers fluoresce strongly. Knowing this can help you detect a forgery or a fake.
- Dating Cloth Items. Cloth items include clothing, stuffed animals, rag dolls, and quilts. Many modern cloth fibers, including sewing thread, are made of polymers like rayon and polyester. These glow under a black light. Items that don't glow might be old and antiques. However, even if they're old, they might glow if they've been washed. That's because modern laundry detergents have additives that glow. So these items need extra testing.
Check items around your home to see what you can deduce about their ages!
NOTE: Standard safety precautions apply -- do not look directly at the black light.
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By Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
January 2014
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References:
About.com Antiques "Ways to Test Antiques & Collectibles with a Black Light" by Pamela Wiggins
http://antiques.about.com/od/resourcesforbeginners/tp/aa122205.htm
