Coffee Developers - Why do they Work?

Discussion in 'B&W: Film, Paper, Chemistry' started by htmlguru4242, Nov 26, 2006.

  1. htmlguru4242

    htmlguru4242 Member

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    I've notices that the various coffee-based developers (specifically "Caffenol LC+C" - [Kudos to Donald Qualls for that one], seem to work very well, especially considering that they're made from coffee and washing soda.

    So, I've been wondering: what is it in the developer that acutally causes it to work? I know that coffee contains, tannins, phenols, a host of acids, and lots of other chemical goodies.

    Can anyone give any chemical insight into this?
     
  2. Photo Engineer

    Photo Engineer Subscriber

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    Tannins and the vitamin C in many of these work. Red wine works for the same reason - tannins. Acorns, boiled in water work if you use the liquid due to the tannins. Read about it in Haist.

    PE
     
  3. htmlguru4242

    htmlguru4242 Member

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    Red wine as a developer?

    This I must try ... and it has to smell better than the coffee concoctions :tongue:
     
  4. gainer

    gainer Subscriber

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    If you drink enough of the red wine, you won't smell the coffee developer.
     
  5. jnanian

    jnanian Advertiser Advertiser

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    LOL !!
     
  6. Gerald Koch

    Gerald Koch Member

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    Coffee contains several chemicals that are derivatives of catechol. This may account for its developing properties. I think that most people consider ability this to be a curiousity more than anything else.
     
  7. Ole

    Ole Moderator Staff Member Moderator

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    Tannic acid was one of the first developers for silver halide emulsions.

    What happens is that developers contain a weak reducing agent which changes the (exposed) silver halides to metallic silver. There are a lot of chemicals that work; but many of them work a little too well and will reduce the unexposed halides as well.

    Some of the stuff in coffee just happens to have reduction potentials inside the useful window.
     
  8. Ryuji

    Ryuji Member

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    I think you mean gallic acid, which is a building block of hydrolyzable tannin.
     
  9. Ole

    Ole Moderator Staff Member Moderator

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    Oops - you're right. An internal translation error, I believe (German -> Norwegian -> English, without involvement of a brain).
     
  10. Jordan

    Jordan Member

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    My understanding is that the primary "developing agent" in coffee is in fact caffeic acid, which is a glycoside of 3,4-dihydroxycinnamic acid (a catechol derivative, as Gerald mentioned). Caffeic acid is structurally unrelated to caffeine.
     
  11. gainer

    gainer Subscriber

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    I haven't tried it, mostly because my brain has other needs for coffee, but I wonder why instant coffee is specified. Is it a matter of convenience, or does it somehow depend on the method of processing of coffee beans to extract the coffee essence? When I drink coffee, I would rather wait on the coffee maker than drink the instant stuff, even Folger's.
     
  12. titrisol

    titrisol Member

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    Well IMHO instant coffee is a lot easier to make 4x strength as needed by cafeinol.
    Besides being el-cheapo of cours e
     
  13. titrisol

    titrisol Member

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    There was a paper from the RIT guys a while ago about this. When my imagination was excited from coffee developers in 2004 I found it, and even got in contact with the professor who explained that caffeic acid in the rpesence of alkali (washing soda) was the main developing agent.
    That is why mint also worked, the bark of a few trees, and a few other plant extracts as well.
    I have that paper somewhere in the storage room and can not give you a reference from the top of my head.

    GEE GOOGLE IS YOUR FRIEND:
    http://www.rit.edu/~andpph/text-coffee.html
     
    Last edited by a moderator: Nov 28, 2006
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  15. derevaun

    derevaun Member

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    Instant coffee typically is made primarily with Robusta beans, which have about twice the caffeine content of Arabica--but I recall that someone here determined that caffeine in place of the coffee doesn't develop film. There are all sorts of bitter flavors in Robusta beans that are absent in Arabica and that make them a bad primary choice for properly extracted coffee, so whatever the developing agent is, it's probably one of the reasons diner fluid taste so bad.

    In any case, if you want to use on-hand commodity coffee instead of going out for instant, you can make it 4x strength by using about 230 grams of coffee per liter of water. Boiling it would probably get the most extraction. Try to make terrible coffee and you'll probably get a pretty good developing agent.
     
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  16. srs5694

    srs5694 Member

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    Out of curiosity, I once tried a mixture of Mountain Dew and sodium carbonate. No dice. As I recall, it actually cleared the film. I have no idea if it was working as a fixer or if it just ate away the emulsion. Probably the latter.
     
  17. Jordan

    Jordan Member

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    I would guess that it's the latter as well.

    Anyway, there's nothing in the structure of caffeine that would suggest that it's redox-active (a necessary condition to be a good developing agent) as is.
     
  18. Ole

    Ole Moderator Staff Member Moderator

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    Maybe that's the reason... Coffee drinkers would rather drink their real coffee, and have finally found a use for the dreadful instant stuff. Non-coffee-drinkers, on the other hand, might as well buy the dreadful instant stuff, since they don't know the difference anyway. :tongue:
     
  19. Photo Engineer

    Photo Engineer Subscriber

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    Since we drink wine and coffee rather than use them as developers, then we should use another of Grant Haists suggestions. Urine is a good developer, according to him. Perhaps it is due to all of the coffee and wine we drink.

    PE
     
  20. Gerald Koch

    Gerald Koch Member

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    So far over 800 compounds have been identified in coffee. Many of these may have developer capability if they are present in sufficient concentration. The principal chemicals appear to be caffeic acid and its esters. BTW, caffeic acid and caffeine are NOT structurally similar and caffeine has no developer properties.

    Just because a chemical is a reducing agent does not mean that it is a developing agent. For those interested I would refer them to a book on photochemistry which will discuss further restrictions on the type of reducing agent. The most recent is by Grant Haist but older books may still have a good explanation.

    Coffee is a far better drink than it is a developer.
     
  21. Photo Engineer

    Photo Engineer Subscriber

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    If a reducing agent is too strong, it becomes a fogging agent.

    Examples include stannous chloride, hydrazine and t-butyl amine borane which have been used as fogging agents in reversal processes.

    Some just fog the emulsion, while others actually fog and reduce at the same time forming silver metal everywhere with no discrimination.

    PE
     
  22. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Well, exactly. I wasn't going to waste good coffee for this, but there was a dusty jar of instant coffee in the back of a drawer somewhere at the office, so I figured this was the perfect use for it, and it actually wasn't that bad as a developer. I suppose that if I were really desperate at some point in the future and couldn't obtain any normal developing agent, it could be tweaked enough to be something like ABC pyro.
     
  23. jim appleyard

    jim appleyard Member

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    I would think that instant coffee is used because it is instant, no brew time. This lets us have more time time more souping film, not brewing. Just a guess.
     
  24. jnanian

    jnanian Advertiser Advertiser

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  25. wirehead

    wirehead Member

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    We've SECRETLY replaced his film developer with FOLGERS CRYSTALS! Let's see if he notices! :smile:
     
  26. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    So I came across this interesting document, while searching for information about the hazards of various developing agents--

    http://potency.berkeley.edu/pdfs/FDATestimonyHerbalMedicine.pdf

    It seems that coffee contains catechol (1.33 mg/500ml), pyrogallol (555 mcg/500ml), and hydroquinone (333 mcg/500ml), where 500ml was brewed from 13.3 g of beans (it doesn't say whether they were robusta or arabica or the brewing method). Caffeic acid (23.9 mg/500ml) is present in much greater concentration than the other developing agents, so if it develops film, it's probably the main factor.

    Out of curiosity, I looked around to see if one could obtain caffeic acid to experiment with as a developing agent, and it's not cheap--$9 a gram from one source, $320 for 250g from another source.
     
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