How Are Photographs Made in Natural Colors? 



Nearer and nearer is the camera coming to 

 perfect representatiftn of the blush of the rose 



By A. Press 



ALL photography depends on the fad- 

 ing of colors when exposed to a strong 

 light. Of course, when a colored 

 body fades, it would not be reasonable to 

 suppose that it still had the precise chemical 

 composition or structure that it had before 

 fading. It is possible in many cases to 

 magnify or accelerate the fading efifects by 

 steeping the partly faded object in a suit- 

 able solution. In photography this process 

 is called developing. After the develop- 

 ment it is only necessary to dip the faded 

 silver bromide plate or paper into a solution 

 of "hypo" which dissolves the unfaded 

 silver bromide and leaves the black or faded 

 variety of silver to give the finished negative. 



Such a negative, however, is not a colored 

 photograph, because silver bromide always 

 fades to black. If a mixture of chemicals 

 could be found in which the components of 

 the mixture faded individually to difTerent 

 colors, then color photography would be a 

 fact and not an experiment involving 

 subterfuges. 



One difhculty has been that silver 

 bromide and its allied salts are found to 

 fade with practically only blue and violet 

 rays of light. Hence, an ordinary photo- 

 graph gives an untrue represent 

 ation of a colored scene, be- 

 cause the photographic plate is 

 blind to all other colors than 

 the blue and violet. Ways 

 have more recently been dis- 



TE.5T CHART 



UNTEftN SLIDE PUTE 



PANCHROMATIC PLATE WITH 

 SENSITIVE SIDE FACING LENS 



AFFECTS 

 LANTERN SLIDE 

 FILM ONLY 



AFFECTS \ " UNAFFECTED BY BLACK 



PANCHROMATIC PLATE ONLY 



The Gurtner method of obtaining two-color effects by means of blue 

 and yellow patches of color on the plates. It is also possible to obtain 

 patches of white and a fairly good substitute for black by this method 



covered of making silver bromide plates 

 sensitive to all colors, but the chief difficulty 

 now is that the silver salts so treated always 

 fade to the same black color. Thus the 

 great problem in color photography to-day 

 is how to give a different color or tone to 

 the different sets of silver grains faded by 

 the differently colored rays occurring in a 

 composite colored picture. 



An exceedingly simple and ingenious 

 method of two-color photography has been 

 devised by Gurtner. Two grades of plates 

 are required. One is a lantern-slide plate, 

 which must be previously stained by 

 means of a napthol orange solution. Such 

 a lantern-slide plate is generally very slow. 

 This plate is then placed face to face with 

 a panchromatic plate in an ordinary 

 camera and exposed through the glass of 

 the lantern-slide plate. 



Turning to the illustration, it will be 

 seen that a yellow patch in the chart 

 photographed will send out yellow light 

 rays that do not fade the silver of the 

 lantern-slide layer because only blue or 

 violet rays can affect it. Such yellow rays, 

 however, in passing through into the pan- 

 chromatic plate can affect the specially 

 treated silver forming the sensi- 

 tive surface of the plate. On the 

 other hand, the blue patch in 

 the chart affects only the lantern 

 film. It cannot pass through to 

 the panchromatic film, since, by 

 staining the lantern film with an 

 orange yellow dye, it effectively 

 stops all blue or violet light from 

 passing through. With the white 

 light again, because it really has 

 in it a mixture of 

 yellow and blue rays, 

 it affects both plates 

 in the camera, 

 whereas the black 

 • patch in the chart 

 affects neither of the 

 corresponding por- 

 tions of the plate. 

 Thus all the blue 

 patches of the chart 

 are photographed on 

 one plate and all the 



