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avandesande
12-06-2006, 11:19 PM
PE, has anyone done comprehensive testing of food dyes for sensitizing activity? I thought an easy way to do this would be to get some ortho film, dip it in the dye and let it dry out...and epose. What do you think?

Photo Engineer
12-06-2006, 11:39 PM
Yes, but AFAIK, the only ones in common use were chlorophyll and erythrosine.

They only work under carefully controlled conditions. Chloroplyll is the least effective of the two from what I understand.

Dipping does work in some cases.

PE

Struan Gray
12-07-2006, 04:49 AM
Food dyes and colours extracted from blackberry juice (and other berries) have been explored by people making dye-sensitised solar cells, a closely-related application. Their main problem is longevity.

Gerald Koch
12-07-2006, 12:06 PM
Just because something is a dye does not mean that it will act as a sensitizer. Sensitizing dyes are very expensive and if there were cheap alternatives then companies would be using them.

Photo Engineer
12-07-2006, 12:42 PM
Gerald, of them all, Erythrosine is quite good as long as you use the right methodology to incorporate it. It is also inexpensive due to its use in anticeptics and as a food coloring agent.

The method of addition to an emulsion varies with the type of halide, whereas the other commonly used dyes are all added using a common method. This is the major problem with Erythrosine and I have worked out two methods of addition for it in two types of emulsion that give good sensitivity.

I have posted the spectral response of a Br/I emulsion here that uses this dye. It is the ISO 40 film (or ISO ~200 paper negative) emulsion in another thread.

PE

avandesande
12-07-2006, 03:22 PM
Thats why I suggested testing. Companies might disregard certain cheap dyes because they aren't very effecient or do not have a great shelf life. I hate to reinvent the wheel but we are stuck with the materials that are available to us.


Just because something is a dye does not mean that it will act as a sensitizer. Sensitizing dyes are very expensive and if there were cheap alternatives then companies would be using them.

Gerald Koch
12-07-2006, 03:26 PM
I based my answer on what was used commercially. I remember having to order a sensitizing dye some years ago for a phys chem class. The smallest quantity we could buy was 1 gram and this cost the university well over $100.

Struan Gray
12-07-2006, 03:54 PM
Perhaps I'll have to try a blackberry emulsion, just to prove a point :-)

The purpose of a photographic dye is to capture light and then to pass the captured energy on to the halide crystal so that it can create a development center. The solar cell dyes I mentioned do exactly the same thing, but with electrode materials like titanium dioxide or indium tin oxide. The principle is the same though, and I would expect them to work to some degree with silver halides.

But not all dyes will do this. Some hang on to the energy. Some no longer absorb effectively when attached to the receiver crystal. Some are incompatible with gelatin. Some mess up the action of developers. Some are highly poisonous. Dyes for colour negative or conventional transparency film are more specialised still, as the bit of dye left behind after it has given up its energy has to play a part in forming the colour in the processed film.

So, the Dyes which allow you to make a medium-to-fast film with a high degree of consistency, a long shelf life and suitable fir a wide range of taking conditions are indeed very specialised chemicals, and expensive to synthesise.

But, dyes which work well enough for a dedicated amateur who otherwise has only expensive or nonexistant options, might be cheaper, more readily available, or even growing on a bush near you.

avandesande
12-07-2006, 04:00 PM
Laser dyes are a little easier to get and have similar functional groups as photosensitizing dyes but tend to be pretty expensive.

http://www.sigmaaldrich.com/Area_of_Interest/Chemistry/Materials_Science/Display_and_Optoelectronics/Laser_Dyes.html

Ole
12-07-2006, 04:03 PM
It would be interesting to know what dyes Herr Dr. Vogel tried and rejected about a century ago, before he finally managed to make an orthochromatic emulsion...

avandesande
12-07-2006, 04:05 PM
This one is right out of "Photographic Sensitivity",
https://www.sigmaaldrich.com/catalog/search/ProductDetail/SIAL/173738

Struan Gray
12-07-2006, 04:08 PM
Laser dyes are a little easier to get and have similar functional groups as photosensitizing dyes but tend to be pretty expensive.

Caution: if you're buying laser dyes without experience of using them, please study the material data sheet and any manufacturer safety recommendations. Many of them are poisonous, carcinogenic, or both. We don't let PhD students handle them without special safety training over and above the usual laser safety course.

Photo Engineer
12-07-2006, 04:28 PM
Silver halide sensitizing dyes are similar to the dyes used by the human eye to affect color imaging. The big difference is that the dyes adsorb to the surface of the silver halide crystal. Of course, there are dyes that form direct, light sensitive salts with silver to give a material that is light sensitive in a given region of the spectrum.

The best dyes are quite complex organic molecules and very expensive to make. Many of them are very toxic to animal life but are used at such tiny levels and decompose so quickly during processing, that they pose no problem. They also have great difficulty entering the animal body due to their very nature, but should be handled with care.

Erythrosine is an exception, being very low in toxicity.

The color of the dye is adjusted during synthesis by changing the number of CH=CH groups in the chanin between two large ring structures, the more, the further towards cyan the dye becomes until it becomes an infra red dye which is rather black. Dyes are the opposite in color to the portion of the spectrum that they sensitize the emulsion to.

I know of no azo dye that is a sensitizer for silver halide. These are dyes formed from N=N moieties.

The foremost researcher into this topic at Eastman Kodak is Paul Gilman. He 'wrote the book' so to say.

PE

rongui
12-07-2006, 07:16 PM
PE, has anyone done comprehensive testing of food dyes for sensitizing activity? I thought an easy way to do this would be to get some ortho film, dip it in the dye and let it dry out...and epose. What do you think?

Here in the US "McCormick Assorted Neon Food Colors" has 4 dyes in the kit. One of the bottles is FD&C Red #3 and from my research on the net is erythrosine.

Hope this helps,
Ron

Photo Engineer
12-07-2006, 07:21 PM
You are correct, but you don't know several things about it.

1. Concentration - this is critical when it comes to adding to the emulsion.

2. Other ingredients - again, critical.

PE

rongui
12-07-2006, 07:37 PM
You are correct, but you don't know several things about it.

1. Concentration - this is critical when it comes to adding to the emulsion.

2. Other ingredients - again, critical.

PE

Hey PE. Thanks for your response.

I guess that the easiest and most inexpensive way to test the effectiveness of this dye is to try it in an emulsion then check for ortho sensitivity and possible negative side effects.

Ron

Photo Engineer
12-07-2006, 08:21 PM
Hey PE. Thanks for your response.

I guess that the easiest and most inexpensive way to test the effectiveness of this dye is to try it in an emulsion then check for ortho sensitivity and possible negative side effects.

Ron

Yes.

Testing is difficult though. You need a spectrosensitometer or multi color step wedge.

PE

Hologram
12-08-2006, 03:19 AM
It would be interesting to know what dyes Herr Dr. Vogel tried and rejected about a century ago, before he finally managed to make an orthochromatic emulsion...

Vogel started his experiments with Korallin. Later, he introduced Eosin and Azaline (mixed of Cyanine and Chinolin red).
The use of Erythrosin goes back to Eder.

Struan Gray
12-08-2006, 06:26 AM
I did some digging in the (online) library, and came up with the attached text from a history of Ilford published by G. B. Harrison in the Proceedings of the Royal Society in 1953.

W. de W. Abney (later "Captain Abney", later still "Sir William Abney") published several interesting papers in th Proc. Royal Soc. in the 1880s and 1890s. He says that analine dyes were tried in collodion emulsions, but were not very successful. He states that the best dyes were the ones most easily bleached (which makes sense from a modern understanding of dye sensitisers). The analine dyes were of course famous for their colour fastness.

Finally, the best explanation I have yet read of how development centres form in a halide crystal and how a dye molecule contributes to the process (as well as what reciprocity failure is and how it occurs) turned up in a beautifully-written and classic paper by Gurney and Mott. Recommended if you have access to a research library:

"The theory of the photolysis of silver bromide and the photographic latent image." R.W.Gurney and N.F. Mott. Proc.Roy.Soc. Vol 164, No.917 (Jan 21, 1938), pp151-167.

Photo Engineer
12-08-2006, 10:50 AM
Struan;

The Gurney and Mott work is a classic well known at Kodak. When we are first hired at Kodak in research we take a very long course in photographic science and engineering, going to regular classes with homework along with our normal job.

We have a huge set of notebooks that teach every phase of this, and the work is accompanied by a lab where we first do hand coatings and then machine coatings. We do color and B&W both.

We used to call it "Ding Dong School".

This two volume set has never been published for obvious reasons, but part of it is in Mees and James and part is in Haist. These are the 'unclassified' parts.

The classified parts contain (among other things) page after page of sensitizing dyes, their properties, their spectra, the best mode of addition, what types of grains to use them on. It resembles the tables in Mees and James, but is more extensive. Gurney and Mott are prominently featured in the section on sensitization. The current version on dyes was written by Paul Gilman.

PE