Need Advice - Exposing Colour Paper to light

[jimmyp82]

Hi

I am hoping someone can advise me on a couple of things. My knowledge of colour printing is very slim so I apologise now if I am asking silly questions -

How is the colour actually formed on the paper? Is it from the wave length of light hitting the paper or the time it hits if for?

I want to expose some colour paper to a light source, its a LED equaliser, so sound will be passed through it, led's jump around (these can be coloured or just white), I want to shine this through some frosted glass to diffuse the light and expose directly onto paper. Is this possible?

I know the filters in a colour enlarger filter amounts of specific wavelengths of light but what is these weren't used at all what would happen?

Thanks for your help
James

 

[koraks]

Your idea will work, but you'll have to experiment to get the result that you're after. Still, it'll work.

The color is formed just like in color film: the paper emulsion has three different layers with in-built filters that make the silver halide sensitive to the correct color (cyan light for red color, etc). Upon development, the silver halide is converted to metallic silver, but the important thing is that as a result, the developer oxidizes and the resulting chemical combines with another chemical (the color coupler) that's also present at the same site. When combined, these two molecules form the dye that creates the color. Since this happens in three layers for all three primary colors, a wide gamut of mixed colors becomes visible. Further processing (bleach fix) removes the developed silver which doesn't contribute to color and hence isn't needed.

 

[MattKing]

Welcome,
The different components - cyan sensitive for red colour, magenta sensitive fo green colour and yellow sensitive for blue colour - of the emulsion on colour paper respond to different wavelengths of light.
So I'm not sure whether what you want to do will work the way you want it to.

 

[koraks]

It will work, but the image will be inverse to the light pattern of the leds. getting the color and contrast right will be the challenge.

 

[Mr Bill]

[Note: I see several responses posted since I started pecking this out,; instead of editing I'm just gonna post as is, even though I'm duplicating some answers.]

Hi, color photographic paper basically has three different color-sensitive layers in it. Each layer forms a different colored dye. The individual dyes are called cyan, magenta, and yellow. The layers form a dye that is roughly "opposite" to the light exposing them, like so: the layer forming cyan dye is roughly sensitive to reddish light; the magenta dye layer is sensitive to greenish light; the yellow dye layer is sensitive to bluish light. The dyes are actually formed by the action of the developer on certain precursors that already exist in each layer - in essence each layer already "knows" what color dye it can form.

It may seem strange that things happen in this seemingly backwards order, but the color FILM also behaves in the backwards manner - the net result is that the two "backward" actions combined end up producing the original color.

Here's roughly what YOU have to do: 1) buy some color photo paper, AND the special processing chemicals (the process is called "RA-4"); it uses a special color developer and a "bleach-fix," each of which you have to mix up according to the instructions. Then you have to take everything into a completely dark room. You make the very-finely controlled exposure, then process (develop, then bleach-fix, then wash) at the proper temperature for the proper time. As a note, processing unexposed paper will result in white paper. Exposing thoroughly to white light, consisting of reddish, greenish, and bluish light, will result in ALL three dyes being formed, appearing black.

In practice one fine tunes the color with small adjustments in the colored exposure. It will be very difficult to control if you don't have some specially designed equipment. As a note, the paper is pretty sensitive - if you were to accidentally turn on the lights in your darkroom for just a second or so, this is probably enough to make the paper go black. And if your exposing light doesn't have the proper color makeup then you won't be able to properly control the results.

 

[lantau]

In practice one fine tunes the color with small adjustments in the colored exposure. It will be very difficult to control if you don't have some specially designed equipment.

That might quite important for the OP. Being a couple of sessions into RA4 now, it answered an open question for me. How is the orange mask of film neutralised. Paper or filters. To me the paper seems to be designed in its respone to largely neutralise the orange mask. The colour filtering on the head is really just fine tuning. When you project the perfectly balanced negative image onto the paper the orange mask is still dominant. It's hard to believe that that unattractive mess will result in such beautiful prints.

So with the shift towards orange lacking in the OPs LED installation I'd expect the final result to have an orange cast, relative to what the OP might want to get. Remember, it's a negative process, so less orange will result in more orange.

 

[1kgcoffee]

Use a lifx colour bulbs. Approximate setting of 331 hue and 0.35 saturation. This should correctly expose most Kodak films onto Kodak ra-4.

 

[jimmyp82]

thank you very much for all the answers so far.

so the exact colours and cast aren't a concern to me. really from the movement of the lights on the LEDs I just want to create a varied and random pattern. I suppose I would like to cut back on the orange tint that has been mentioned and would probably prefer the majority of the paper to turn black with some areas showing colour.

If I placed a sheet of orange plastic between the paper and my LED light source would it cut back on the orange tint?

thanks
James

 

[koraks]

The paper is balanced somewhat to correct for an orange mask, so without the mask the paper tends more towards red/orange (remember that you get the inverse color of the light you throw at the paper).
To get a predominantly black sheet, you'll have to make sure most of the sheet gets a lot of light, save for the areas where you want some color, which you should expose less. In other words, you'll have to cobble something together that exposes much of the paper to quite a large amount of light and expose the remainder with the much fainter light of your moving leds. Some sort of masking will probably come into play.

 

[John51]

It would be easier and cheaper to practice with b+w paper first. At least it should get you in the ballpark for when you try RA4.

 

[koraks]

Easier, yes. Cheaper, not all that much. Color paper is ridiculously cheap if you think about it. Particularly if you cut from rolls yourself.

 

[ic-racer]

If you get the paper right up to the display, your photogram might look like this. If the display is active (bouncing up and down), it will look like the one on the left. If the display is static, it will look like the one on the right. This is a GREEN LED display:

 

[John51]

Easier, yes. Cheaper, not all that much. Color paper is ridiculously cheap if you think about it. Particularly if you cut from rolls yourself.

Cheaper per print but only if you do loads of colour prints.

Minimal start up costs for b+w: 25 x Ilford MGIV 5x7 =£7.98. Ilford PQ universal developer = £7.54. Tetenal Superfix Plus 250ml = £4.89. If you want to stay with Ilford, their Rapid Fixer 500ml = £8.49. About £20 to get started in b+w.

 

[koraks]

Yeah, startup costs are steeper for color. But still, it's not outrageous. I would consider the color route from the start if that's what OP is after.

 

[jimmyp82]

If you get the paper right up to the display, your photogram might look like this. If the display is active (bouncing up and down), it will look like the one on the left. If the display is static, it will look like the one on the right. This is a GREEN LED display:
View attachment 216816

that is super interesting thanks for that!

i think i will be looking for colour darkroom facilities near where I live to do some tests.