Screen-Plate Print - Autochrome on Paper - Dye-Couplers, DTR and some luck...
People have repeatedly brought up the idea of utilizing the screen-plate technique (red, green & blue screen) for prints. The problem is that a screen-plate is inherently an additive process, where the RGB elements are backlight and fuse to create colors when seen at a sufficient distance, just like a color television. All elements create white, no elements create black, and every thing in between creates, well... everything in between.
The problem with paper is that we need to utilize reflected light, not transmitted light. Ergo, we need to use cyan, magenta & yellow. However, if the whole page is covered with CMY elements in a screen arrangement we have simply created a black piece of paper!
The key then is to lay down color only where there is image density, allowing paper to constitute the whites and varying degrees of CMY to make up the image, just like a color halftone. But how on Earth can we achieve this via the autonomous mechanisms of photography? Here's an idea...
Imagine that we have a RGB screen and in each separate element there is a mixed a corresponding color coupler. All the red spots would have a cyan coupler intermingled, the blue would have a yellow coupler and the green a magenta.
Adhered to this screen would be a panchromatic emulsion on paper with a diffusible base, for letting the chems through. Upon developing, the exposed areas would develop silver, oxidise the developer and create a dye with the coupler. If the dye could be made to migrate or imbibe to the paper surface, color would only be laid down in proportion to the amount of silver present and thus unexposed areas would remain paper white. The paper could then be peeled away from the plate to reveal a color print.
The obvious issue is that this would create a negative. Hmm...
Alternatively, lets imagine this coupler-RGB screen is coated with a panchromatic emulsion. By utilizing diffusion transfer reversal (DTR; early patent here... like in instant film, and discussed over at New55) perhaps we can create a positive in the first go.
In addition to the screen & a thinly coated panchro emulsion, there would be a "nucleating sheet", which is basically the business end of an instant print product. In the presence of developing agents, the negative film will diffuse out its unexposed halides to this sheet and in turn, create a positive. If we can get the dye couplers to go through the emulsion and into the receiver sheet as well, we'd get a one-off positive color print from a screen-plate.
Is this practical? I'm going to go with... no! But, it's a novel concept that just might work. Take it for what you will.