.. ensations can be produced this way, including those red-blue mixes (purples and magentas) not found at any wavelength band in the spectrum. In photography, the principles of additive color synthesis underlie making separation negatives for photomechanical reproduction of color images, and dye transfer and similar printing processes. It was also the principal behind the Autochrome film process and similar screen processes.
In the darkroom, additive color printing uses red, green, and blue exposures to obtain prints from color negatives and transparencies.( 1 ) The Grainmaker filter relies on this principle of additive color printing. AUTOCHROME was a photographic transparency film patented in America, June 5,1906 (No.
822,532) by Auguste and Louis Lumire of Lyons, France (FR.Pat.No. 339,223, 1903). Like other techniques of the time, it employed the additive method, recording a scene as separate black and white images representing red, green and blue, and then reconstituting color with the help of filters. To do this on a single plate, the Lumires dusted it with millions of microscopic (avg.
size 10 to 15 microns) transparent grains of potato starch that they had dyed red (orange), green and blue (violet). ( 1 ) This screen of grains worked as a light filter to interpret the scene when the light passed through them exposing a panchromatic B&W emulsion. The exposed plate was then processed reversal resulting in a transparency. The illustration below is from their American patent application. Glass was coated with liquid pitch (def.1) mixed with a small percentage of beeswax (to help keep it tacky) then the prepared grain was dusted on.
By this very action, the resultant screen was stochastic (or random) in nature. In order to comply with the first black condition (def.2) it was necessary to fill the spaces between the irregularly shaped grains. Lampblack was used as a filler, applied by way of a special machine. The result is shown in the enlarged illustration below The starch was probably (facts are a bit sketchy) dyed using triphenylmethane dyes (note 1) to achieve a color wavelength of between 550 to 670 for the red, 470 to 570 for green, and from 430 to 520for the blue.
Later, the Lumires discovered the transmission quality of the plates could be improved by applying pressure (5000Lbs.per sq. inch (3) to the composite prior to the addition of lampblack. Potato starch grains are not flat, but somewhat rounded, and in my opinion, their method of elutriation (def.3) contributed to the puffy condition of the starch.
The next stage in construction was to coat the composite with liquid shellac to totally encapsulate the grain layer (in essence, forming an envelope of amber around the grain). After drying, the panchromatic B&W emulsion was then coated on the composite plate and the final plate was soon ready for market. The plate was exposed in a glass plate type view camera by placing it in the holder with the coated side away from the lens, so that when exposed, the light traversed the glass, through the grain and exposed the light/color sensitive emulsion from the back. After exposure, the plate was processed to reversal in an acid dichromate type process.
The final photograph has a beautiful look with wide tonal gradation and if you could see an original well preserved Autochrome today, you would be amazed at the extrodinary way they age, and can in fact appear as though they were processed only yesterday. The image below is an original Autochrome, photographer unknown. This filter is the only one of it’s type in the world. Used for introducing the appearance of enlarged grain in color photographic prints. The appearance of grain created is a true representation of the color inherent in the original.
Unlike texture screens that work by breaking up the image using a patterned blocking mask such as Kodalith film (tm Kodak), this process works by projecting a normal photographic color negative thru a handmade additive color synthesis stochastic screen comprised of millions of grains of transparent potato starch. The starch is dyed to two specific wavelengths then mixed to uniformity and coated on a glass plate. Printing is achieved by utilizing a custom glass carrier for enlarged grain imaging or projected thru a coated glass plate that is in contact with a receptor paper. From subtle to radical effects are possible, while maintaining the contrast of the original and the ability to control color. To learn how this process was invented and how we make it, go here.The Grainmaker color filter system was designed to introduce the appearance of grain in color photographic prints by using dyed transparent potato starch coated on a glass plate as a filter through which a color negative is projected.
Several steps are involved in its construction as outlined below. The first step is to size the starch; I use a pharmaceutical raw product service to separate the starch down in size to 15 microns or less because the larger grains are unsuitable for this use. The dyes used are commercial and pharmaceutical varieties of triphenyls.
(food coloring will not work) The starch is dyed using an air driven device to blow the dry starch into a continuously agitated container of liquid dye kept at a temperature of 90 F until its the consistency of syrup. (The starch must be blown in or else it dyes unevenly.) The wet starch is then poured into trays to dry.Several days later, the dry starch is pulverized and re-filtered, then mixed to uniformity in a baffled tumbler The colors used are very important and as shown in the enlarged illustration the colors are cyan/green and yellow/green in nature. Through a number of tests I determined these colors worked the best with color negative paper to yield a neutral gray with direct enlarger exposure.
If you can achieve a neutral, all colors are possible within the limits of the material. As you can see, I chose not to fill the interstices with lampblack for two reasons, first, I don’t have access to any drawings on the construction of the special machine used by the Lumieres in their autochrome process, and second, it seems to work fine without it. The next step is to prepare the glass by using a machine of my design to cover the plate evenly with a custom made adhesive as shown in the illustration below.By passing the knife blade (yellow) over the adhesive spreads it evenly, then the wet plate is attached to a centrifuge and spun at 1000rpm to smooth it out, its then left to dry for several days until the adhesive sets up.
Finally the mixed grain is dusted on, and it receives a coating of epoxy sealer. The plate is now ready for use. The plate is inserted into a glass carrier grain side up and the color negative is placed in this modified carrier in the usual way. The print is made by projection through the screen resulting in the appearance of natural grain, only more so. COLOR is a phenomenon of perception not an objective component or characteristic of a substance.Color is an aspect of vision; it is a psychophysical response consisting of the physical reaction of the eye and the automatic interpretive response of the brain to wavelength characteristics of light above a certain brightness level (at lower levels the eye senses brightness differences but is unable to make color discriminations). ( 1 ) That light is the source of color was first demonstrated in 1666 by Isaac Newton, who passed a beam of sunlight through a glass prism, producing the rainbow of hues of the visible spectrum.
This phenomenon had often been observed before, but it had always been related to latent color that was said to exist in the glass of the prism. Newton, however, took this simple experiment a step further. He passed his miniature rainbow through a second prism that reconstituted the original white beam of light, His conclusion was revolutionary: color is in the light, not in the glass, and the light people see as white is a mixture of all the colors of the visible spectrum.( 2 ) The reason rainbows appear colored is because the light is broken down into its constituent parts by passing through the water droplets in the air.
(Sorry, no pot of gold. The perception of color in a rainbow is proportional to the viewer’s perspective, you move, it moves.) The theory of color has gone through some changes over time, and it is now an accepted fact that color is truly in the eye of the beholder. This is due to the fact that, as sensed by man, color is a sensation and not a substance. ( 3 ) Different people can also see color differently.
We all agree the sky is blue, but a piece of reflective art may look slightly blue to one person while another sees it as slightly cyan. If you don’t know the difference between the look of blue as opposed to cyan then communicating your preferences to a technician can be problematic. Subtle color variances are best seen under correct viewing conditions (not by a window, etc.
) and can take some time to learn to even see them. Then when you can both see and discern these differences, then comes the task of communicating your choice for correction to a technician in the right terms (something I will cover soon). Science Essays.