Chemistry Project

Discussion in 'The Darkroom' started by stingray, Jul 15, 2006.

  1. stingray

    stingray TPF Noob!

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    I'm in year 10 at a school here in Melbourne and we've been given pretty much free choice over what to do for this semester's research project. We were encouraged to do something that interested us so I immediately thought of photography and then development of film.
    I have decided I will do something to do with different quantitieis of developing agents in a film developer. I can then carry out everything the same (agitation, times, film and subject, printing and analysis) and just change the quantity of metol or hydroquinone...
    I'm just wondering if I can get some advice on where to start with regards to which formula i should use and what quantity increments to go by.. how much more or less than the "recipe" before i'll notice any great difference.
    THanks a lot in advance for your help.
    Will.
     
  2. stingray

    stingray TPF Noob!

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    bump...
     
  3. Torus34

    Torus34 No longer a newbie, moving up!

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    Could be interesting. One problem will be to decide how you're going to measure the effects - microphotographs of the grain, densitometer readings, etc..

    A good old standard developer is D76. The formula is in the public domain and readily available:

    Water, 125F/52C 750 ml
    Metol 2 g
    Sodium Sulfite (anh.) 100 g
    Hydroquinone 5 g
    Borax (granular) 2 g
    Cold water to make 1 L

    The sulfite and borax provide buffering. The correct pH is as important to the development process as the metol and hydroquinone. [It's also why acetic acid stops the process cold.] The chemical equations for buffer concentration are straightforward.

    If you're lucky, Herst van Rental will spot this post and provide comments. If so, pay attention and take notes!
     
  4. Hertz van Rental

    Hertz van Rental TPF Noob!

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    Much as I hate to be a wet blanket with people exhibiting an enquiring mind I have to say that I think the experiment you intend is a bit of a non-starter.
    I understand your thinking - more or less developing agent in the dev will give more or less development.
    I'm afraid it doesn't work like that.
    Whilst neat developer will work quicker than diluted developer (basic Chemistry: increased concentration of reactants = increased rate of reaction), altering the amounts of the developing agent in the dev in relation to everything else is not the same thing.
    To understand this you have to know what the various components of the dev 'soup' are doing.
    Developing agents on their own (Metol and Hydroquinone are the commonest, Phenidone is similar to Metol in most respects) are actually not very good at developing film. They can take an hour or more to produce a useable image - and they tend to also develop unexposed silver halide, raising base fog levels.
    If Metol & Hydroquinone (MQ) or Phenidone & Hydroquinone (PQ) are used then a superadditivity effect happens where the results are far superior to using just one of the components on it's own (which is why these are the commonest dev types).
    Also included in most dev formulae is an alkali - the development reaction is a RedOx one so increasing the alkalinity of the dev will speed up the process.
    A preservative is also included. Most developing agents when dissolved in water begin to react with dissolved oxygen and decompose. The solution quickly turns brown, loses it's development properties and can cause emulsion staining. Most developing agents produce quinols as part of their decomposition process and these quinols work as decomposition accelerators. Inclusion of something like a sulphite inhibits the catalytic properties of quinols to extend developer life.
    In addition some developers have 'restrainers' or 'improvers' in them to cut down the development of unexposed silver halide. A common one is Potassium Bromide - although one of the by-products of development is soluble Bromide so this isn't always necessary.
    The amounts of the various chemicals present in a developer are calculated to give optimum performance. By altering the concentration of one of the constituents the balance is shifted and a range of unpredictable effects are possible. The one certain effect is that the efficiency of the developer will be reduced.
    One also has to ask the question 'what will you be measuring?' and 'how will you measure it?'
    The only accurate and objective way to measure changes to a neg is by means of a densitometer. But how are you going to check for something like developer decomposition?
    A simpler and easier experiment would be to alter the pH of the developer. You can then work out the rate of reaction at various pH levels and ascertain at what pH development stops.
    If you shoot a test target and standardise the development you should be able to produce a visual comparison on a selection of negs.
    You could also try seeing how much development times need to be changed in various pH levels to get the same result as development in standard pH.

    Whatever you decide, though, the very best of luck.

    PS I suggest you read here before you start (if you haven't already).
     
  5. fightheheathens

    fightheheathens TPF Noob!

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    im not an expert on film developemnt, but i do have a degree in chemistry, which allows me to make several general statements in addition to what Hertz van Rental said.

    developement of film is an extreamly complex reaction, more so if we are talking about color film. As someone who has done research chemistry, one thing i can tell you is that film developing chemistry has been researched to exhaustion. When this whole developement thing came about, (this extends to all modern developers) first some chemist had an idea about a better way to develope film. This idea would then be put into practice in the lab. Usually when something if first thought up, the first order of business is to get the reaction to work. It doesnt matter how good the results are, just that you have results. For example, at first your reaction gets only a 2% yield of the expected product. But it works. Then the next step is to optimize the reaction...ie get the yield up to 99%.
    same in film developement chemistry. First they found a way to get some developement, then they optimized it.
    What this means is that some unsung chemist has fiddeled with this developement formula, probably for several years. Any combination you can try has most likely been tried and found to be inferior to what you are sold.

    that said, if you do want to experiment and you are gona change things,
    change only one thing at a time and go by whole numbers.
    IE double one reagent or 1/2 one reagent etc, it gets complicated when you start changing things by .435 etc.
     

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