170 THREE-DIMENSIONAL PHOTOGRAPHYNeither the base nor the image is effective alone. Only the com-
bination of the image made up of crystals of the proper type with
the optically active base will produce the effect, It need hardly be
added that the crystalline structure is not visible to the eye. The
images have the full quality of any fine dye transfer print.
The normal Vectograph is a transparency. If it is desired to be
used as a print, the back is coated with a solution of very fine
aluminum powder in a suitable vehicle. The aluminum serves the
same purpose as the white paper in an ordinary print, but to pre-
serve the essential polarization it is necessary to have this reflect-
ing layer of metallic material. Hence the aluminum.
However, the Vectograph is at its best as a transparency. In
relative large sizes, 8x10,^1 1x14, or larger, and placed in an il-
luminated frame, Vectographs form one of the most striking of
stereo exhibits.
The Vectograph would be ideal for home movies if it were not
for the complex mechanical installation which would be neces-
sary. Also the quintuple film footage would boost costs, one
double length negative, two positives and a transfer base-that is,
assuming that the original negative is exposed with alternate right
and left frames. The only practical solution would be through
central laboratories such as those used now for normal film
processing.
There is no such disadvantage with the still picture. Any com-
petent amateur can quickly learn to make good prints, and if he
happens to be versed in dye transfer already, he has very little
to learn.
The negative is made with an ordinary stereo camera. Enlarge-
ments are made on washoff film and developed in warm water. In
this step, one negative is reversed so that the prints are mirror
images of each other; placed face to face, they correspond. The
two images are carefully aligned vertically. Lateral alignment is
based upon normal stereo separation. The films are hinged to-
gether book-form with adhesive tape, then immersed in the spe-
cial dye bath. The two films are removed from the dye bath,
rinsed and the special base sheet inserted between the two, and
the whole run through a photo wringer. The base sheet is stripped
off, with one stereo image on the back and one on the front.
Viewed with 3D goggles, the image is seen in full stereo relief.