[Grainmaker specifics]

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.

[Illustration showing enlarged Grainmaker grain]
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.

[Coating device]

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.

I'm always interested in discussion, scientific or otherwise. You can Email me at jscruggs@bway.net

( additive )( autochrome )( color )( film )( screens )( subtractive )