Note M — Chapter XIII

Pictures produced in the three primary colours are extremely crude. Dr. Vogel has proposed a large number of negatives, using for their production sensitisers corresponding with every region of the spectrum. For example—Napthol blue for red, cyanin for orange, rozin for yellow, and fluorescein for bluish green, the ordinary sensitiveness of the plate being sufficient for blue and violet, the latter, however, being exposed through a yellow screen. The images thus obtained are printed from lithographic stones or Collotype plates, each of which is printed in a colour complimentary to that part of the spectrum to which the particular plate was sensitive. The greater the number of separate images produced in this way the more complete will be the reproduction of the various shades in the original, and the more pleasing the resulting print.