Color film for VERY long pinhole exposures?

[danube]

Howdy folks,

I am new to this group and have an interesting question, though I might offend some because a computer is involved.

I am taking some "solargraphs" by the method described by Justin Quinnell, who has been discussed here as well (google him for more details). A piece of black and white photo paper is exposed in a pinhole camera for days to months exposure. When the film is removed from the camera, a VISIBLE negative image is recorded on the paper. The paper is then scanned quickly with a digital scanner and further processing is done on the computer. It's really an ingenious technique.

One of the neat things about it is that despite using black and white paper, some COLOR is rendered by the process. After negation, the sun is yellowish and the background often a blue tint. I doubt there is much spectral information recorded, but perhaps the color is proportional to exposure. If someone could explain the physics behind the process, that would be welcome.

But my question is this: What would happen if I were to use COLOR photographic paper as my "negative"? Does it work in the same way as black and white paper does? I presume it is much faster, but after a few days exposure, would there be a visible image recorded that could be scanned if only once? Does color paper exposed to light even get dark?

I'd like to see what folks think before investing in a box of color photographic paper. Even on e-bay it's getting expensive. But with fall colors coming out, it would be nice to get some subtle hints of color in my pinhole shots.

Thanks, and I look forward to your replies.

Dan

 

[paul_c5x4]

Tried RA4 last year in a pinhole coffee tin in an attempt to do just what you described. No it doesn't work.
However, if you really wanted to give it a go, (depending on where you are) I can mail some small bits of RA4 paper - Say half a dozen scraps about 6"x4".

 

[holmburgers]

One of the neat things about it is that despite using black and white paper, some COLOR is rendered by the process. After negation, the sun is yellowish and the background often a blue tint. I doubt there is much spectral information recorded, but perhaps the color is proportional to exposure. If someone could explain the physics behind the process, that would be welcome.

Ok, I wrote this description, then realized you said "black & white" paper, but I've heard of a pin-hole project that literally just used black paper, and the image is formed by fading. So that's where all this came from.....

.....This is a very old phenomenon, noticed early in the history of photography. It has some analogues to Uto paper, but I'm not qualified to draw any at the moment (analogies that is). Here's my best crack at explaining this....

Blue light from the sky hitting the paper will appear blue, right? Therefore, that paper is reflecting blue and absorbing every other color of light. By absorbing everything else, the paper is taking in that energy, not bouncing it back, so it has a damaging/fading effect. I'm sure when you get down to the physics, it's bumping electrons off or something to that effect (I really have no idea).

So the colored light is destroying the elements of the dye in the paper that don't reflect blue light, and after a long enough time, you are left with a color.

Now, I'm struggling to make sense of this myself, but I've read about it and this should put your head in the right ball park to understand it. I've got some books that have great explanations of this... I'll do some searching on Google books in the meantime.

update: ok, here it is from J.S. Friedman's 'History of Color Photography'...

A yellow dye appears such because the ultraviolet and blue rays are absorbed, and the green and red rays are trasmitted unaffected. A yellow dye will fade, therefore, only when it is exposed to blue or UV light. A magenta dye will absorb the green rays, hence its sensitivity will be limited to the green range. A cyan dye will absorb the red rays, so its sensitivity will be confined to that region. If a yellow, cyan and magenta dye be mixed in equivalent portions, the yellow will absorb the blue, the magenta will absorb the green and the cyan the red. Together, they will absorb all the visible light. If the dyes are fugitive and bleach upon exposure, a very interesting phenomenon results. Suppose we expose the mixture to blue light. This will affect only the yellow dye, since only that will absorb blue (we assume ideal dyes), and thus only the yellow dye will fade or bleach, dependent upon the length and intensity of exposure. If all the yellow dye be bleached, there will remain an equivalent mixture of the cyan and magenta dyes. The cyan will absorb the red primary and transmit the blue and green. The magenta will absorb the green primary and transmit the other two. Only the blue primary will be transmitted by both acting simultaneously. Thus an exposure to blue will yield blue. A similar analysis will show that, regardless of what the color of the exposing light is, the resultant image will be as close an approach to it as is possible under a 3-color subtractive system utilizing these dyes as secondaries.

We have to assume that the black paper used has some mixture of dyes in it.

 

[danube]

Tried RA4 last year in a pinhole coffee tin in an attempt to do just what you described. No it doesn't work.
However, if you really wanted to give it a go, (depending on where you are) I can mail some small bits of RA4 paper - Say half a dozen scraps about 6"x4".

Howdy. How long were your exposures and did the film register *anything*? For Ilford MG-IV an exposure of a week's worth of sunny days is sort of a minimum for a reasonable image. A couple months gives an image with good density. I'd love to try it if you haven't already explored the same parameter space. However, I'm in the US.

Thanks for the reply.

Dan

 

[danube]

Yup, Black and White film! Very strange that color comes out of it. I'm speculating, but I was thinking along the lines of silver crystals being precipitated out by such a long exposure, and if there are enough of the correct size, they could absorb longer wavelengths, giving a blue tone were very exposed (and yellow when inverted). But that is merely speculation on my part.

Construction paper is a neat Idea. I've thought of trying that when I noticed that sheets left in the closet for years get brown when exposed. Newspaper might be a bit faster though. It yellows in a matter of days when exposed to bright light.

Dan

Ok, I wrote this description, then realized you said "black & white" paper, but I've heard of a pin-hole project that literally just used black paper, and the image is formed by fading. So that's where all this came from.....

.....This is a very old phenomenon, noticed early in the history of photography. It has some analogues to Uto paper, but I'm not qualified to draw any at the moment (analogies that is). Here's my best crack at explaining this....

Blue light from the sky hitting the paper will appear blue, right? Therefore, that paper is reflecting blue and absorbing every other color of light. By absorbing everything else, the paper is taking in that energy, not bouncing it back, so it has a damaging/fading effect. I'm sure when you get down to the physics, it's bumping electrons off or something to that effect (I really have no idea).

So the colored light is destroying the elements of the dye in the paper that don't reflect blue light, and after a long enough time, you are left with a color.

Now, I'm struggling to make sense of this myself, but I've read about it and this should put your head in the right ball park to understand it. I've got some books that have great explanations of this... I'll do some searching on Google books in the meantime.

update: ok, here it is from J.S. Friedman's 'History of Color Photography'...

A yellow dye appears such because the ultraviolet and blue rays are absorbed, and the green and red rays are trasmitted unaffected. A yellow dye will fade, therefore, only when it is exposed to blue or UV light. A magenta dye will absorb the green rays, hence its sensitivity will be limited to the green range. A cyan dye will absorb the red rays, so its sensitivity will be confined to that region. If a yellow, cyan and magenta dye be mixed in equivalent portions, the yellow will absorb the blue, the magenta will absorb the green and the cyan the red. Together, they will absorb all the visible light. If the dyes are fugitive and bleach upon exposure, a very interesting phenomenon results. Suppose we expose the mixture to blue light. This will affect only the yellow dye, since only that will absorb blue (we assume ideal dyes), and thus only the yellow dye will fade or bleach, dependent upon the length and intensity of exposure. If all the yellow dye be bleached, there will remain an equivalent mixture of the cyan and magenta dyes. The cyan will absorb the red primary and transmit the blue and green. The magenta will absorb the green primary and transmit the other two. Only the blue primary will be transmitted by both acting simultaneously. Thus an exposure to blue will yield blue. A similar analysis will show that, regardless of what the color of the exposing light is, the resultant image will be as close an approach to it as is possible under a 3-color subtractive system utilizing these dyes as secondaries.

We have to assume that the black paper used has some mixture of dyes in it.