Is chlorophyll a sensitiser?

[ZorkiKat]

I read that Ducos du Hauron (ca 1870s) used chlorophyll extracted from plant leaves to render his plates sensitive to red for his early colour experiments. The plates were soaked in the chlorophyll solution - the same manner that other experimentors did to make their colour-blind plates sensitive to green and red, but in other dye sensitisers- when ortho or panchro emulsions were not yet common. Would doing the same i.e, soaking ordinary bromide paper in chlorophyll solution make it red sensitive? Chlorophyll extraction is a common highschool biology experiment.

Jay

 

[Donald Qualls]

You'd probably need to add the chlorophyll when making the emulsion, and there's a major drawback: it'll turn your paper green, probably indelibly (ever tried to get a grass stain out of clothing?).

 

[Ryuji]

Would doing the same i.e, soaking ordinary bromide paper in chlorophyll solution make it red sensitive? Chlorophyll extraction is a common highschool biology experiment.

Chloropyll is a very different dye from the kind of dyes commonly used in modern photographic emulsions, and I don't have experience with it.

Applying a dye to a coated and dryed emulsion by immersing the material in a dye solution is an acceptable approach when low adsorption density of dye is sufficient, such as infrared plates. But for most visible light plates, you probably want to maximize the adsorption of the dye. This is best achieved by adding the dye before coating.

I don't know if chlorophyll sensitizes or desensitizes your test emulsion. The dye may add sensitivity to red light, but it may also decrease the intrinsic sensitivity to blue light, called desensitization. A same dye may behave differently with AgCl and AgBr emulsions. The mechanism underlying this phenomenon was only very recently elucidated, and it requires good background of solid state physics (material science) to understand it. Modern sensitizing dyes are so highly specialized area of dye chemistry.

My guess is that, while chlorophyll may be a good experiment to prove something can be done, it is probably not a very practical choice. For practical purposes, I recommend you choose from what's known to sensitize AgBr with minimal desensitization effect. Most modern sensitizing dyes are selected from a class of dyes called cyanine dyes.

If you want to try chlorophyll anyway, I recommend to use silver chloride emulsion such as Azo paper, and use methanol solution of the dye.

 

[Kirk Keyes]

use methanol solution of the dye.

In the EPA method for Chlorophyll analysis, it is extracted from plant materials with a 10% Water and 90% Acetone solution.

 

[Ryuji]

Sure, acetone-water mix would work to dissolve chlorophyll, but I don't know if I want to use acetone to apply dye by immersion. One would have to test. The solvent has to be something that can deliver the dye through the gelatin matrix, and also rather quick to dry.

I use acetone for a couple of organic synthesis that I have to do in darkroom (for emulsion making), but I generally prefer other solvents, such as ethyl acetate, 2-propanol, etc. when water is not good.