PROGRESS IN COLOR PHOTOGRAPHY—SMILLIE. 935 
the silver salt, which is still unreduced behind the granules that were 
impervious because of their color to the light rays which impinged 
upon them in the original exposure. The green granules have now 
become transparent because of the solution of the reduced silver which 
covered them. After this immersion the plate is exposed to white 
light for a short time and again developed. This time the red and 
violet are covered by an opaque layer of reduced silver from the 
second exposure and development. 
Thus by this double exposure and inversion we get the true colors 
of the object from the unobscured granules, and not only this, but the 
effect on the eye is one of continuous and homogeneous color, as the 
granules are so small that rays of light from contiguous grains reach 
the eye confused together. 
The process may be stopped at this point and the plate used as it 
comes from the second development, after being dried and varnished 
for protection. The plates are generally subjected to a process of 
reenforcement, however, which strengthens the colors and makes them 
more brilliant. If this reenforcement is carried through, the plates 
have to be “ fixed ” after the second development. This fixing weak- 
ens the tone of the colors so that the reenforcement has also this loss 
to make up. If the plates are not reenforced, this fixing should be 
omitted on account of the consequent weakening. 
The illustration accompanying this article was made with the 
ordinary commercial Auotchrome plate, and reproduced by the half- 
tone process. 
THE WARNER-POWRIE COLOR PROCESS. 
L. Ducos du Hauron in his patent of the year 1868 outlined a proc- 
ess of preparing a three-colored screen consisting of bands of three 
primary colors in juxtaposition, which screen was to be placed before 
the sensitive plate when making the exposure. The full importance 
of Ducos Du Hauron’s suggestion was not recognized until Joly in 
England and MacDonough in America, within a very short time of 
each other, proceeded to apply it in practice. The Joly screens were 
ruled with agueous colored inks upon a glass support coated with a 
thin layer of gelatine, and, although of the somewhat coarse ruling of 
two hundred bands per inch, were capable of producing results of con- 
siderable delicacy. The difficulty, however, both with the Joly and the 
MacDonough screens, lay not in the use, though this suffered from cer- 
tain limitations, but in their manufacture. The mechanical operation 
of filling a glass plate with three series of lines of different colors 
without gaps or overlap was a technical problem which, in the way 
in which it was approached by both concerns manufacturing the 
screens, proved impossible of realization on a commercial scale. 
