Weird Paper Question

[htmlguru4242]

B&W Paper Question - this is odd...

I was experimenting today with the fact that ordinary photo papers (I was using Kodak Polycontrast RC) can print out in bright sunlight. I noticed that a sheet of the paper would go form its normal white color to a dark purple-black in the sun in about 5 - 10 seconds. I left it out for about 30 minutes, just to see what would happen. (Obvioulsly, it continued to darken. Hoever, it was a little windy, so I placed a piece of heavy translucent red plastic on each side to keep it down. To my incredibly surprise, whe I brought it in about 30 minutes after that, the area under the red plastic was slightly red in color?!?!? I then placed the paper under blue plastic, and it wasslightly blue. Orange - masked C-41 negs. imparted a blue-purple color.

Any idea why this is, or am I completely imagining colors here?

 

[kenh]

Hum, no idea. Very interesting. I am going to have to try this.

One of the manufactures indicated that there are developers built into the paper to reduce the required development time .. however the color thing is really odd.

 

[htmlguru4242]

I know it's odd. It's certainly barely color, but its definetely there...

After doing some research, I have noted that in hte 1800, william Herschel noticed this with silver chloride paper blackened into the sun (as it turns out, this relates to my earlier post on heliochromy...

 

[Donald Qualls]

Different grain sizes due to different levels of senstivity to different light wavelengths.

The red light is causing much slower printing-out (the paper is almost insensitive to red), which lets the grains grow larger from fewer centers and, as with a warm tone developer, shifts the balance toward red. The opposite is true of blue -- and you get some of both, and a more neutral tone, with unfiltered daylight. Why it goes blue-green under an orange C-41 mask -- well, probably that film lets enough green pass that the effect of the green light (to which the paper is MUCH more sensitive) predominates over the red (to which the paper is almost blind).

Well, it's a theory, and one that makes physical sense. I'm pretty sure it'd take an electron microscope to be sure whether it's right or wrong...

 

[htmlguru4242]

That sounds good... However, the aper was completely blackened before placing the colored plastic over it. The un-covered areas did not blacken any more...

 

[Donald Qualls]

Okay, there's only one possible reply to that:

Hmmmmmmmm...