A NOTABLE ADVANCE IN COLOR PHOTOGRAPHY. 



525 



of an old theory by ruling glass screens with infinite fineness and accu- 

 racy and in breaking up the original negative into three, from which 

 plates can be made to print on ordinary paper. 



All makes of ruled polychrome screens can be used to obtain the nec- 

 essary negatives for the Sampolo-Brasseur process. The best are those 

 ruled in lines in groups of threes, one line being in a reddish orange 

 color, one in a yellowish green, and the other in a blue-violet color. 

 These colors may vary somewhat, as the dry plates of different makers 

 are not equally sensitive to the various colors of the spectrum. In 

 case of a serious departure from these colors, corresponding changes 

 nnist be made in the printing inks used. 



The screens made by Mr. Brasseur have 581 lines per inch, with no 

 mistakes in any inch of more than one fifty-thousandth of that space. 



Having obtained the necessary negative, a positive on glass is made. 



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Fig. 3.— Black and 

 white screen placed 

 over positive and show- 

 ing only one of the pos- 

 itives. 



Fig. 4.— First step in 

 making negative. Only 

 one-third of the plate 

 is covered, and prints 

 from this could not be 

 properly superposed. 



Fig. 5.— Completed neg- 

 ative of one of the im- 

 ages. Entire surface is 

 now occupied by image 

 which on original only 

 occupied one-third. 



This positive is apparently no different from ordinary positives, but if 

 it ])e examined under a microscope it Avill be found to consist of three 

 interwoven images, corresponding with the three sets of lines of the 

 taking screen. (See Fig. 1.) 



Suitable printing plates must now be made from each one of these 

 interwoven images. This is done ])y placing a black and white screen 

 (fig. 2) over the positive in such a way as to hide two of the images 

 and leave only the third one visible, say the yellow. (Fig. 3.) A half- 

 tone negative is made of this (see fig. 4), and during the exposure the 

 most important step occurs; the negative plate (see fig. 4) is moved 

 continuously until the image which occupied the one-third of the plate 

 occupies the entire surface. (See Fig. 5.) 



This is essential, as to obtain the proper colors the prints must be 



superposed and not juxtaposed, as they were in the original positive. 



The screen (fig. 3) is now shifted the width of one line, covering up 



the image ol which a printing plate has been made and exposing a new 



gM 1900 3T 



