Introduction
Longwave black light is a range of light invisible to human
eyes. While it cannot be seen, black light makes many materials
fluoresce, or give off visible light. The fluorescence varies
in color and brightness. Materials can fluoresce white, yellow,
orange, blue and other colors. The fluorescence can be bright
to dim.
Fluorescence under black light has a wide variety of practical
uses and in a wide variety of areas. Memorabilia collectors and
dealers use black light to identify fake trading cards, postcards
and prints. Historians use black light to help date glass, porcelain
and paintings. Medical doctors use black light to identify and
treat medical conditions. Police detectives use black light in
homicide and car crash investigations. The government uses black
light to authenticate drivers licenses and currency. Artists
use black to create glow in the dark posters, paintings and theatre
sets. The list goes on and on.
This article is an introduction to longwave black light: what
it is, how it works, how it is used and how you can use it.
What is longwave black light?
Longwave light is a part of the light spectrum, the entire light
spectrum ranging from X-rays to infrared light. In between X-rays
and infrared light include visible light (the light humans can
see) and ultraviolet light. Common nicknames for ultraviolet
light are invisible light and, as used here, black
light. Ultraviolet light got these nicknames as the light
is invisible to humans. In a dark room ultravioloet light is
invisible or black.
There are two types of ultraviolet light used by humans: shortwave
and longwave. This article is only about longwave black
light. Shortwave is useful in areas, including in identifying
postal stamps and gem stones, but is more dangerous to use. Used
properly longwave black light is safe for kids and adults.
What is black light, the tool?
common style of hand held black light
To use black light, you need a black light, the tool. This
tool is a light that emits only, or mostly, black light. Black
lights are sold commercially come in a variety of sizes and styles.
Many look like conventional lights and flashlights. Some are
small enough to fit in your pocket. They are sold in a variety
of places, including rock shops and eBay. A good black light
can be purchased for under $20. The average collector purchases
a handheld size and AA battery powered. Remember to make sure
the light you are purchasing is longwave, not shortwave. Luckily,
most models sold are the safe longwave.
How to use a black light
Examination of material with black light must be done in the
dark, whether in a dark room during the day or at night. It is
best to be in the dark for a couple of minutes to acclimate your
eyes. When you're ready, turn the black light on an shine the
black light on the material. Most black lights emit a small mount
of visible light so that you know it's on.
It's best to examine a material against something that does
not fluoresce. If the background gives off light it may effect
the results.
If you have a black light, you can shine it around your house
in the dark and see lots of things that fluoresce. Some around
the house things that often fluoresce include computer paper,
laundry detergent, eye glasses and modern postcards.
How Does Black Light Make Things Fluoresce?
The fluorescence, or visible light that is emitted from a material
when black light is shined on it, happens at the atomic level.
Just as with light, heat and x-rays, black light is a form
of energy. When black light is shined on a material, whether
the material is glass, plastic or paper, energy is being added
to the atoms of the material. The atoms can only hold this extra
energy for a short amount of time before having to give it off.
The atoms give off the energy in a different form than received.
The atoms receive the energy as black light, but may give the
energy off as heat, ultraviolet light, infrared light, visible
light or, often, a combination of these. What form(s) of energy
the atoms gives off is dependant on the makeup of the atoms.
If visible light is emitted by the atoms, that is the fluorescence
we see. The color of this visible light is also dependant on
the atomic make up. If the atom gives off just heat, ultraviolet
light or infrared light, there will be no fluorescence. In a
darkened room this material will remain dark.
Phosphorescence
Some materials phosphoresce under black light. This means that
the material gives off visible light but after a time delay.
This produces an after flow that can for seconds or more.
How does black light help collectors, historians and others
The color of fluorescence for a wide variety of materials
is known, and the person with a black light can make sure an
item fluoresces the color it is supposed to. For example, collectors
of Lelique glass use black light to identify if it is vintage
or the less expensive modern. Antique Lelicque glass fluoresces
a bright yellow under black light, while the modern version does
not. The collector doesn't have to be an atomic chemist to test
the glass, just know the colors of fluorescence.
* * * *
Examples of practical black light uses:
The following are assorted examples of how longwave black light
is used in collecting, art, industry and more. There listed in
no particular order.
Dating Laliqeu art glass
The Frenchman Rene Lalique produced some of the finest glassware.
Lalique art glass from before 1945 fluoresces yellow, but not
after
Rene Lalique glass rooster card hood ornament
under visible light.
Authenticating Vaseline glass
Vaseline glass is popular form of glass that is yellow-green.
Under black light genuine Vaseline glass fluoresces a bright
green. Different glass that resembles but is not Vaseline fluoresces
differently, including peach, orange or less bright lime green.
Identifying Old and Modern reproductions of Burmese Art
Glass
Old Burmese art glass fluoresces a bright yellow, while modern
reproductions do not.
Dating American colorless pressed glass
American colorless pressed glass made from before 1925-30 fluoresces
bright. Modern reproductions do not.
Identifying modern reprints and forgeries of antique sports
cards, postcards, programs, documents and other paper ephemera
A black light is effective in identifying of many, though not
all, modern paper stocks.
Starting in the late 1940s, manufacturers of many products
began adding optical brighteners and other new chemicals to their
products. Optical brighteners are invisible dyes that fluoresce
brightly under ultraviolet light. They were used to make products
appear brighter in normal daylight, which contains some ultraviolet
light. Optical brighteners were added to laundry detergent and
clothes to help drown out stains and to give the often advertised
`whiter than white whites.' Optical brighteners were added to
plastic toys to makes them brighter and more colorful. Paper
manufacturers joined the act as well, adding optical brighteners
to many, though not all of their white papers stocks.
A black light can identify many trading cards, posters, photos
and other paper items that contain optical brighteners. In a
dark room and under black light optical brighteners will usually
fluoresce a very bright light blue or bright white. To find out
what this looks like shine a recently made white trading card,
snapshot or most types of today's printing paper under a black
light.If paper stock fluoresces very bright as just described,
it almost certainly was made after the mid 1940s. It is important
to note that not all modern papers will fluoresce this way as
optical brighteners are not added to all modern paper. For example,
many modern wirephotos have no optical brighteners. This means
that if a paper doesn't fluoresce brightly this does not mean
it is necessarily old. However, with few exceptions, if a paper
object fluoresces
Identifying counterfeit sports cards
When place side by side with the genuine card, most reprint and
counterfeit trading cards will fluoresce differently. This is
because the reprint and counterfeit is made out of different
material.
Dating American colorless pressed glass
American colorless pressed glass made from before 1925-30 fluoresces
bright. Modern reproductions do not.
Identifying restoration to art and memorabilia.
Many items are restored by the addition and/or subtraction of
substances. Items that are restored include furnature, paintings,
trading cards, prints and photos. The restoration can change
the value of the item. A longwave black light can identify much
restoration as the added glue, paper or paints can fluoresce
differently under black light.
Detective work
Detectives use black light to identify body fluids at crime scenes.
Black lights are often used to find dead bodies in lakes and
streams, as much clothing fluoresces brightly under black light.
As antifreeze glows under black light, detectives use black lights
to study car crash scenes.
WWII airplane maps
During World Ward II, airplanes from different countries used
maps written in fluorescent ink. At night, the navigator could
read the map without illuminating the cockpit.
Make a black light painting
There is paint designed to fluoresce in different colors under
black light. For best viewing in your room, a longwave black
light bulb might be best. The bulb can be put in a regular lamp.
You can also make sketches and art using invisible ink pen or
other fluorescent materials from around the house. Vaseline and
laundry detergent are just two around the house things that fluoresce.
Invisible ink pens and stamps
There are pens and stamp pads that use invisible ink. The ink
is invisible under normal daylight, but fluoresces brightly under
black light. People use invisible for a variety of practical
uses. People write their name or identification number on valuables,
like paintings and china, so they can be later identified in
case of theft or dispute
An online seller 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 item before shipping she can be sure that the
customer is returning the original items.
Hand stamps for dance clubs, bars and concerts
Clubs often stamp the hand of patrons with invisible ink. This
allows the patron to leave and return, while allowing the club
able to identify those who have not paid the cover. It would
be difficult for someone who hasn't paid to reproduce the stamp.
Authenticating drivers licenses
Many state drivers licenses have printing that fluoresces under
black light. My driver's license has a bright orange symbol under
black light. This invisible marking will help identify forged
licenses.
Marking important baseballs
For identification purposes, Major League Baseball put a fluorescent
stamp on the ball Barry Bonds hit for his record 73rd home run
in 2001.
Find pet urine in the house
Animal urines fluoresces
Finding rats and mice
As rat and mice urine fluoresces under black light, exterminators
and biologists trace the rodents with a black light
Finding Scorpions in the Dark
Many scorpions fluoresce under black light
Identifying baseballs with autographs removed
Some dealers and collectors remove autographs from baseballs
for aesthetic or financial reasons. For example, a single signed
Joe DiMaggio baseball can be worth more than the same ball with
the bat boy's signature beneath. There is one or more companies
that will remove autographs. While the removal may be difficult
to see under normal daylight, the restoration shows up under
black light.
Seeing and photographing sea animals
Jellyfish and some other deep sea fish fluoresce under black
light. Black light is sometimes used to make these animals fluoresce
in tanks.
Detecting ringworm
Ringworm is a fungus that can cause skin problems in pets, and
occasionally is caught by the pet owners. About half of ringworm
can be detected with a black light, with the fungus fluorescing
green. Other types of ringworm does not fluoresce. A laboratory
test of the culture is needed to verify the black light test.
Identifying porcelain
Hard paste porcelain will fluoresce a deep blue or purple color.
Soft paste porcelain will fluoresce white.
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