Evening star., 1924-08-23

| ing the sensitive retina.
1t will be understood that the fad
ing of colorS is not due wholly to
ultraviolet light, since fading takes
place where no direct sunlight falls;
but common observation shows fading
takes place more rapidly in these
places within doors which receive di-
rect sunlight and still more rapidly
out of doors, where there is no glass
through which the rays must pass.
That fading can be accelerated to
such an extent by artificial means
that the results of hours are equ1Va-
lent 10 the natural effect of weeks
or months, is one of the facts estab-
'ished by the study of the action OF
the intense ultraviolet radlatlons
now procurable through the agency
of the electric current.
Artificial Fading Processes.
This rapid fading action is now
being utilized as test for the per-
manency of colors produced by dyes
and pigments. by means of a novel
piece of apparatus, which is in effect
an artificial fading machine, called
the Uviarc cabinet, which has been
developed in the laboratories of the
Cooper Hewitt Electric Company.
This apparatus consists of lamp
contained in a fused quartz tube SIN
inches in length, which emits an in
tense fiux of the ultraviolet rays.
Clear fused quartz is one of the new
substances that is transparent to
ultraviolet radiations. BY using il
as the container for the luminescent
mercury vapor the ultraviolet rays
pass through, and are available for
The many special uses for which
nodern science has found them valu-
able.
one of the first purposes to suggest
itself for the Uviarc (ultra-vlolet
arc) was the use of these rays for the
rapid fading of colorS produced by
dyes or pigments. affording thus
quick test of their stability or fast
ness. When a salesman assures a
customer that a piece of goods is "all
WOOL" it behooves him to know
whereof he speaks; a few threads un-
raveled form the sample: test tube,
little caustic potash and water, and
the truth or falsity of his statement
is soon made manifest.
Takes Day to Insure Test.
When he further affirms it is fast
color" he now needs to speak with
equal knowledge and veracity.
Call this time tomorrow and !
will tell you just how fast the color
is" replies the buyer. Whereupon ne
SENDS the sample TO tne testing ldDO-
ratory of the establishment, where it
passes the ordeal of the 'Uviarc cabi-
net" This is a neat, self-contained
apparatus, provided with apertures in
which part of the sample may be
exposed to the direct action of the
powerful ultraviolet rays from this
lamp for any desired period of time,
after which the sample is removed
and the difference in hue or tint be-
tween the exposed and unexposed sec
tions of the fabric examined.
The relative rates of fading pro-
duced by the "Uviarc" and by sun
light, having been previously deter
mined by carefully conducted tests,
the stability of the color under aver
age conditions of exposure to light
may be calculated with a sufficient
degree of accuracy for commercial
purposes.
Whenever color is used as an ad
junct in manufacturing cloths and
fabrics of every kind. in wall papers
and tapestries, in color printing, in
paints of every description, the use
of this positive test of permanency is
another step toward efficiency and
economy in production through the
avoidance of mistakes that only a
long duration of time could other
wise correct.