Rotogravure process is an intaglio
method of printing, meaning that the pictures, designs and words are engraved
into the printing plate or printing cylinder. Acid is used to cut the
images into the plate. Once the copy is photographed, positives are then
made from the negatives. The images are transferred to the printing surface
by use of carbon tissue covered with light-sensitive gelatin. The gelatin
hardens based on the amount of light that passes through the positives.
The plate or cylinder is then bathed in acid, which eats through the gelatin
squares. On the printing press, the deepest cells retain the most ink
and the darkest tones.
The earliest of card stock materials,
including lobby cards, inserts
and window cards, utilized this process
until the 1920's. After this time, most of these materials were being
printed using a new process known as photogelatin
or collotype printing.
