96 
HOUSE AND GARDEN 
February, 1913 
ture of the glass, and the pleasing appearance of 
such globes and their diffusive properties is en¬ 
tirely dependent upon the nature of the glass and 
its surface treatment. 
In a totally enclosing globe of ordinary clear 
glass, the outer surface of which has been ground 
or etched with acid, there is apparent a brilliant 
spot of light in the midst of an illuminated area 
of less intensity. The microscope and camera 
combined were utilized by the writer in studying 
the phenomenon of light transmission in various 
media and it was noticed that the effect produced 
was to allow light rays to pass through the glass 
without changing their direction. It is well to 
realize that with either an electric bulb or incan¬ 
descent gas mantle, the greatest candle power is 
obtained from the side of the lamp, the greatest 
radiating surface being there. Naturally from 
the tip or base, where the radiating surface is less 
and there is much impediment to light rays in 
the form of metal sockets or burners, the light is 
weakened. Gas or 
our light source 
Source brightness must be sub¬ 
dued to avoid obliterating 
the delicate etching of such 
glassware 
electric lights are 
therefore rated 
by their horizon¬ 
tal, or side candle 
power. Hence the 
electric lamp 
which gives six¬ 
teen candle power 
on the horizontal, is rated as a six¬ 
teen candle power lamp, despite 
the fact that the candle power 
from the tip downward (when the 
lamp is in a pendent position) is 
but 6.6. The bright spot light, 
tells us beyond dispute that the 
greatest candle power is on the 
horizontal and nowhere else 
In a room of average 
with the 
without diminishing it appreci¬ 
ably in quality, the spot light effect will still re¬ 
main as long as ground glass is used. It is a 
question, therefore, whether it is not preferable 
to choose the lesser of the two evils by placing 
over the lamp proper a diffusing cylinder of opal 
glass, thereby entirely concealing from view the 
ugly source, beneath the pleasant suggestion of 
a luminous cylinder, soft and mellow in tone. 
When a totally enclosing globe of opal glass 
was placed over the same source of light used 
with the ground glass globe giving the spot light 
effect, it was evident that instead of a brightly 
visible spot of light against a blurred, obliterated 
background we had a uniformly luminous out¬ 
line. Therefore, any design, or detail on the sur¬ 
face of the glass, in bas relief would be unim¬ 
paired from distortion by ‘‘spot light” effect. 
Opal glass has the advantage of a smooth, yet 
depolished surface, and does not collect dirt 
like ground glassware, with its rough exterior. 
Phosphate glass, 
Fixture arms at this angle are 
incorrectly placed; the globes 
expose the lamps 
like opal, holds in 
suspension innum¬ 
erable particles of 
an opaque white 
color. Most ordi¬ 
nary opal glass- 
w are resembles 
phosphate glass, 
with the exception that the sus¬ 
pended particles in the former are 
often visible, and are flake-like and 
blotchy in appearance. 
Another grade of this glass, 
a r 
ceiling 
typical fixture drop, such 
globe would allow the greatest amount of light to pass 
directly toward the side walls, causing an annoying- 
glare or reflected light from picture glasses, and leav¬ 
ing the extreme upper and lower portion of the room 
in a stratum of darkness. There is positively no ex¬ 
cuse for the use of ground glass in any form with 
modern illuminants. With the older and more sub¬ 
dued types of light sources the spot light effect was, 
of course, less aggravated. 
For example in the Colonial lamp so often seen there 
is an appropriately formed globe upon which a de- 
The best effect with glass 
prisms is obtained when 
used in conjunction with 
amber film 
sign is cut, the background being ground. 
Now, with an oil flame, while there is slight 
visibility of the source, it is entirely natural 
and therefore good. 
Even with a small sized electric bulb of 
4he carbon type the effect is passable, since, 
at least, the amber quality of light sub¬ 
consciously suggests the thing which is 
lacking. But with a tungsten lamp we have 
a brutal glare, so painful to the eye that one can¬ 
not regard the lamp without squinting, and all the 
beautiful detail of the design is lost. 
While the use of the amber gelatine film, pre¬ 
viously described, will modify the color value of 
known as Etruscan opal, is being- 
offered by several glassmakers, 
with a granite surface treatment, 
rich in expression. Several excel- 
^_^ lent imitations of carved ala¬ 
baster bowls have been quite 
beautifully rendered in 
pressed form. Their effect when lighted is beautiful. 
In choosing glassware it requires no expert to dis¬ 
tinguish ground from opal glass. Invariably with 
ground glass there is the glaring spot light effect, de¬ 
spoiling the beauty of design or ornamentation and 
distracting the eye. Opal glass is known by its soft, 
pleasing diffusion, and concealment of source. It is 
only in its cheapest and most translucent forms that 
there is any visibility of source, and then this defect is 
only apparent at close range. 
utility, it is interesting to know 
that opal glass, by virtue of its suspended 
opal particles, has the property of redirect¬ 
ing light, even when in the form of totally 
enclosing globes. The light redistribution 
tends to assume the form of the globe. 
Thus, a sixteen candle power lamp, giving 
more light on the horizontal than from the 
tip downwards- or base upwards, when 
placed within a ball of opal glass will have 
its distribution of light modified by the opal ball, so 
Bend the fixture arms to that it will be more uniform, and, like the ball, more 
redistribute light, but nearly spherical. That is, in the case of a baie lamp 
use more suitable hanging pendent where the greatest lisht was in the 
glassware ( Continued on page 152) 
From the angle of 
