Color images from black and white paper

April 16, 2010 7:09 AM

Color images be made from exposing black and white paper for long periods of time. Can you please explain the chemistry behind how this works?
posted by vostok to Media & Arts (5 answers total)

They aren't really color images-- the paper just takes on a tint as the exposure progresses. What is happening on the paper, where an image appears without developing, is a phenomenon called printing out. Paper specially formulated for this use was in wide use long ago and available subsequently as a niche product but has gone off of the market in the last decade or so. The image isn't permanent, and further light exposure or fixation will bleach it out; on the special paper the use of a toner was required to stabilize the image. I haven't seen anyone properly stabilize those pinhole solargraph images on modern paper; the strategy seems to be to scan the image as quickly as possible before it bleaches off.

As to the actual chemistry of what's going on, I'm not going to be of much help. Try asking over at the APUG forums; there seem to be a number of very knowledgeable chemists over there who could provide some answers.
posted by monocyte at 7:47 AM on April 16, 2010

It's a chemical reaction in response to whatever comes in contact with the paper. It's the same reaction as what happens with the Calotype process, invented By Henry Fox Talbot, which used a salted POP paper. The chemistry has changed since then, but its the same idea.
posted by squeak at 8:08 AM on April 16, 2010

No real details and my google-fu is failing me...

It is possible to get different "colors" from B/W paper by getting the silver crystals in the paper to "grow" in different sizes...
I don't remember the details (it's been ~25 yrs since I did it), but I seem to recall using some chemical baths other than the normal ones. Basically, putting the paper in the developer; sticking it in another bath; then back to developer; etc; etc;
posted by crenquis at 8:32 AM on April 16, 2010

You can always take color photos with B&W film using three cameras. Each camera would have a different color filter in front of the lens.
posted by malp at 10:07 AM on April 16, 2010

crenquis, the process you describe sounds like lith printing.
posted by squeak at 5:07 PM on April 17, 2010