Black
Light Testing
Black light testing is a common practice used to authenticate
antiques. For many beginning collectors, the science and
techniques used in the black light testing method are a mystery, this
article hopes to address this issue.
Blacklights are used in evaluating antiques because the ultraviolet
rays they produce react differently to different materials. Because of
this interesting characteristic, things that are invisible to the naked
eye become visible under the blacklight.
Before we go any further, a word of warning: Be sure that the
blacklight you purchase is a longwave blacklight. Shortwave
blacklights can damage your eyes and skin.
Now, onto the uses of blacklights in collecting antiques. Different
chemical properties become apparent under a blacklight, modern paint
will fluoresce under a black light, older paints will not, you can use
this to determine whether a painted object is an antique or a newer
reproduction as well as to determine whether a piece has been
"touched up" and if so, how extensive was the repair.
The same technique can be used to detect repairs on antique porcelain
as the old finish will not glow under a blacklight, and the newer
material in the repair will.
Some antique glassware will glow under the blacklight as well,
vaseline glass will glow because it contains uranium oxide.
A blacklight can be used to test many types of antiques. Here are
some examples:
Cut Glass: Authentic American Brilliant period cut glass
fluoresces yellow; reproductions have no reaction or show a blue-white.
Editor's Note: This appears to be in debate, we recently
received an email from a member of the American Cut Glass Association
who informs us that "American Brilliant cut glass does not show
yellow with long wave black light - it shows either pale violet or pale
blue. More modern shows bright blue, almost electric. We have over 300
pieces and only one shows yellow and it is a European (English) piece.
The use of black light with cut glass is HIGHLY controversial even among
ACGA folks. Some swear by it, others say it is unreliable. I'm with the
latter school as it is well known that many US cut glass houses had some
of their blanks made in England and some even in Bohemia - this of
course shoots the only American cut glass fluoresces a certain color
theory all to the devil!!"
Cast Iron: Most new paint on most new cast iron fluoresces;
old paint on old cast iron rarely fluoresces. You can also detect newly
painted repairs as well.
Paper Products: Most paper products--like post cards, books,
signs, photos papers, etc.--made before the late 1930s-WW2 era rarely
fluoresces. Paper products made since 1950, however generally fluoresces
brightly due to large amounts of chemical bleaches and dyes.
Pattern Glass: Nearly all American colorless pressed glass
made before ca. 1925-30 fluoresces yellow; reproductions generally do
not have any fluorescence.
Textiles: Thread and Cloth: Synthetic fibers--rayon,
polyester, etc. made since WW2 all fluoresce. This allows you to detect
new military uniforms, new quilts, new doll clothes, etc. Even if old
fabric is used to repair an old quilt, the new thread will fluoresce.
Editor's Note: We received an email from Alan Kelchner, a
professional quilt restoration specialist who added the following
information: "A quilt from 1800 may actually fluoresce, while a
quilt made in November 1998 may not. Mass produced laundry detergents
from the current and past decades have contained additives that make
your laundry whiter and brighter. These additives can make textiles
fluoresce under a black light, which would lead a person to believe an
antique quilt/textile, washed in these detergents, was newly made. And
while many newly made fabrics and threads do fluoresce, there are also
fabrics and threads whose manufacture do not cause it to fluoresce.
Man-made fibers available in the Depression era can be found in all
sorts of vintage quilts from that era. They are very collectible, and
the use of fiber content to label them new is poor information for the
novice collector.
A collector must learn their textile field and be knowledgeable.
Blacklighting is definitely a poor way to confirm a textile's age."
Art Glass: Lalique before 1945 fluoresces yellow; after 1945,
it does not. Genuine old Burmese fluoresces bright yellow green, new
reproductions do not.
Porcelain: Hard paste porcelain will fluoresce a deep blue or
purple color. Soft paste will fluoresce white.
NEED
A BLACK LIGHT?
If
you'd like to purchase a blacklight, we recommend you visit the
Black Light Shop website. Different types, sizes and prices
available to suit your needs.
NEED MORE INFO ON BLACK LIGHT TESTING?
For additional detailed information on black light testing, we suggest
The Black Light Book for Antiques & Collectibles.
It will help you detect reproductions, faces and repairs. Contains
103 photos and illustrations, and 112 pages of text.
