PE.. Food dyes

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by avandesande, Dec 6, 2006.

  1. avandesande

    avandesande Member

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    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?
     
  2. Photo Engineer

    Photo Engineer Subscriber

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    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
     
  3. Struan Gray

    Struan Gray Member

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    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.
     
  4. Gerald Koch

    Gerald Koch Member

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    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.
     
  5. Photo Engineer

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    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
     
  6. avandesande

    avandesande Member

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    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.

     
  7. Gerald Koch

    Gerald Koch Member

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    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.
     
  8. Struan Gray

    Struan Gray Member

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    Perhaps I'll have to try a blackberry emulsion, just to prove a point :smile:

    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.
     
  9. avandesande

    avandesande Member

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  10. Ole

    Ole Moderator Staff Member Moderator

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    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...
     
  11. avandesande

    avandesande Member

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  12. Struan Gray

    Struan Gray Member

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    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.
     
  13. Photo Engineer

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    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
     
  14. rongui

    rongui Member

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    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
     
  15. Photo Engineer

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    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
     
  16. rongui

    rongui Member

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    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
     
  17. Photo Engineer

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    Yes.

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

    PE
     
  18. Hologram

    Hologram Member

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    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.
     
  19. Struan Gray

    Struan Gray Member

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    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.
     
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  20. Photo Engineer

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    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
     
  21. avandesande

    avandesande Member

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    After looking into it a little more, it appears that the vinyl linked heterocyclic compounds stick to the surface of the silver grains which is why so little is needed. Other dyes may work but not very efficiently.
     
  22. avandesande

    avandesande Member

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    Are you referring to "The theory of the photographic process"? In your opinion would it be possible to put together a 'good enough' dye package using the published tables?

     
  23. Photo Engineer

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    It is nitrogen in the heterocyclic ring that attaches to the surface AFAIK. And, they can stack up in groups called "J" aggregates based on the work of Dr. Jelley at Kodak. This shifts sensitivity to longer wavelengths.

    So, a green sensitizer can form a "J" aggregate and become a red sensitizer. These types of dyes are well known for strong adhesion to the surface of an emulsion. I believe that the red sensitizer in Kodachrome is actually a green sensizer that has formed a "J" aggregate. At least, that is what I seem to remember.

    PE
     
  24. Photo Engineer

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    Yes, by Mees and James. This was the final edition of that book.

    IDK, I never studied their tables well enough. Kodak used to sell about 15 dyes from that list at quite reasonable prices, but no longer sells them. I fortunately have a complete set now and can make a pan film. It took me nearly 3 years to get there though.

    I don't intend to make a pan film as it is too difficult to do at home.

    PE
     
  25. Struan Gray

    Struan Gray Member

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    Lets hope the notebooks eventually make it into the public domain as Kodak adapts to a digital world. (Or doesn't). I know that some of my collaborators' collaborators on the solar cell basics got money from Fuji on a regular basis, so fundamental research still goes on. Some of the modern forms of X-ray spectroscopy and my own field, tunnelling microscopy, have allowed a more detailed understanding of both how the molecule attaches to a crystal, and how the charge transfer occurs.

    Neville Mott was the grand old man of the lab when I was doing my PhD. I met him several times, but never talked about anything substantial. The only photographic connection I had was listening to the lab photographer gently complain that he was being repeatedly asked to make copy prints of a Vatican photo of Mott meeting the pope.