Evening star., 1924-08-23
EXTENDED USE OF COLORS
Marks MODERN COMMERCE
Demands Make Permanency of Dyes and Pigments
Matter of Importance-Tin,e Tests Too Slo'o
for Rapid-Fire Necessities.

The varied and extended use of
col>rs in articles Of everyday use has
made the permanency of color in dyes
and pigments matter of great prac-
tical Importance to industry. The or
dinary test of tim" is entirely too
slow for the rapid fire necessities of
modern commerce. VIII this colored
fabric fade in three months? Three
months from now competitor will
have the trade: one must know to-
morrow! VIII this naint fade in two
years? In five? The owner OF the
house Will not wait that long to see.
he is going to start painting next
week. The two greatest chemical re-
agents in existence are water and
light. Chemists are of the opinion
that there is probably no substance
that is absolutely insoluble in water
and no compound that is entirely i'm
mune to the chemical action of light
Chemical change in Il substance very
generally produces a change in color:
hence the tendency OF all things eX-
posed to light to fade
In general sense one speaks of
any change in color as fading; but in
the Stricter sense the word refers to
the tightening of the color by the in
crease of white in its compassionate
other words, the disappearance of
color. Change in tint, however. is
always more or less in evidence in
all cases.
Violet Rays Most Active.
1t is now known that the radia-
tions which are incapable of produc-
ing the sensation of vision, and whi,'
are commonly known as the ultra
violet" rays, are the most active
agents in the process of fading These
rays are present in sunlight, and are
chiefly responsible for tan and sun
burn-though tan is not a fading, but
a darkening of the skin produced by
the human laboratory as a protection
against the destructive effect of the
powerful ultraviolet rays
The sources of artificial light that
have done service through the ages.
the flames of burning fats and oils,
do not produce these invisible radia-
tlons. 1t was not until the electric
light came into use that ultraviolet
rays were mingled with the visihl
rays in appreciable quantities. The
oculists have suspected that the pres
ence of these rays in the modern
forms of electric light might prove
injurious to the eyes, but their fears
are not well founded
Since sunlight contains these rays
to a large extent, the eye must have
developed a sufficient means of self
pIolttlItIl, or general pilnineSS "Oulu
have ensued The explanation is
simple; substances which are quite
transparent TO light rays are nearly
or wholly Opaque to ultraviolet rays
Ordinary glass, and more especially.
glass containing lead, intercepts a
large proportion of ultraviolet radia-
ton. The various media of the eye.
through which radiations must pass
before impinging upon the sensitive
retina, which transforms light-enerGy
into the nerve currents which pro-
duce the sensation of vision, are
equally Opaque to these rays.
EycbaII Acts as Ray Filter.
The contents of the eyeball which
are both solid and liquid, act as a
ray-filter. which normally allows only
such radiations to pass as the nerve
mechanism is fitted to receive and
translate into consciousness. 1t is
only when other light radiations are
present in excessive amount that they
can penetrate this armOr with sufti-
cient force to produce injury to the
living tissues. This may happen with
sunlight from a clear sky reflected
from snow or ice. Clouds, fog and
atmospheric impurities serve as an
effective screen against undue
amounts of ultraviolet light reach