Different temperature coefficients for different developing agents

Discussion in 'B&W: Film, Paper, Chemistry' started by edtbjon, Mar 8, 2009.

  1. edtbjon

    edtbjon Member

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    Since I begun developing my own films I've used the tables and graphs published by Kodak, Agfa or Ilford, to find the correct developing time if my temperature differed from the standard 20 deg C. Last week I stumbled upon a very comprehensive, but old book (1956) on photo chemistry. (A swedish book called "Fotografisk kemi" by Artur Boström.)
    To the interesting part: The author doesn't give a lot of explanation on this, but there seem to be a difference in how various developing agents react to a change in temperature. This was quite a revelation to me. Not that it doesn't make sense, because it does. It's just that noone have really pointed this out before (to me that is). I havn't really had any problem with this either, but on the other hand, I didn't use Pyro and Pyrocat developers until the last 3-4 years.
    The facts from the book are (roughly translated from swedish):
    "In general you state the temperature dependency by giving the temperature coefficent, i.e. that number which tells how much quicker the process is at 10 deg (C) rise of temperature. The more temperature dependent a developing agent is the larger the temperature coefficent. This is for:
    Metol 1.3
    Paraminofenol 1.5
    Metol-hydrokinon 1.9
    Hydrokinon 2.0-2.5
    Glycin 2.3-2.6
    Pyrocatechin 2.5-2.8
    ..."
    (A table feature in the editor would be nice. :smile: )
    Anyhow, it's the last line in the table which makes me react. Even though e.g. Pyrocat HD uses a mix of Hydroquinone and Catechin, the table above gives me a hint that Pyrocat developers are more sensitive to a change in temperature than e.g. D-76. Also, Pyrocat-HD should more sensitive than Pyrocat-MC.

    Do I have any question? Yes, as I first don't really get how to use the coefficent in practice. D-76 should be a standard Metol-hydroquinone developer with a coefficent of 1.9, but looking at e.g. the Ilford table they seem to use a higher coefficent (like 2.3 or so). Now you might say that I got my facts wrong, which is possible, but given the quality of the rest of the book, I recon that the author (Mr. Boström) does have the facts right.
    It would be nice if some of our knowledgeable experts on the subject of developing agents would like to cast some more light on this issue.

    //Björn
     
  2. ic-racer

    ic-racer Member

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    Perhaps PE will see this and chime in, but I believe that just having a 'factor' for the developer is only one-half way toward a time-temperature table. You would need a corresponding factor for the individual film. We had a long thread on this a while back and I concluded that empirical test of each developer/film combo are needed, however some generalizations can be made for groups of developers and films.
     
  3. Photo Engineer

    Photo Engineer Subscriber

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    Well, firstoff there was a long thread about this very subject a short while ago.

    Second, I really don't think that the simplistic approach will do, as rate also depends on pH and buffer capacity as well as sulfite content. And, these are also affected by temperature.

    I personally think that the tables are better than factors. In addition, where are ascorbic acid developers, phenidone developers, dimezone developers and etc.... So simple data such as you post are too incomplete to be truly useful.

    Just my $0.02! (for you non US readers - my two cents worth)

    PE
     
  4. edtbjon

    edtbjon Member

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    I've been around the 'net long enough to know the value of two cents. :smile:
    First, I've been reading this and other sub-forums of Apug for a few years now, but I must have missed out on the threads you mention. ( ... or I wasn't really ready for them ...) A quick search did indeed give me the threads you mention. (It should be this one: http://www.apug.org/forums/forum37/52337-developer-temperature-compensation-formula.html back in July -08. I must have been on a heavy work schedule back then...)
    To give PE and ic-racer some kind of answer, I recon that back in 1956 the table was rather complete. (In the thread linked above DF Cardwell refers to a similar source and table from a book written in 1955. Now, I like 1956 better, as I was born then. :smile:) Besides, while the book is comprehensive from an amateur point of view, there is also an indication of the intended audience, i.e. the amateurs of 1956. (Since when general knowledge of these matters have deterioated very rapidly.)
    Anyhow, before the translated quote from the book I said that the author didn't give a lot of explanation on the subject matter. It seems like I have to 1) thorughly read the rest of the book, and 2) make my own testing...
    ... as I realize that both the recommended times from e.g. Ilford are "starting times" and that the compensation charts (tables or graphs) which are issued by again e.g. Ilford are recommendations.
    At least I now do know where to look for more information on the matter.

    Finally, this posting was more a matter of curiosity than an actual problem. I bought a Jobo a few years ago to take care of any inconsistensy problems as such.

    //Björn
     
  5. Photo Engineer

    Photo Engineer Subscriber

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    Well, to add to my previous post, many developing agent combinations are superadditive and also are influenced by reaction with sulfite, so just assigning a figure to Metol-Hydroquinone of 1.9 is misleading as the ratio of the two is important as is the ratio of HQ to Sulfite as is the ratio and absolute values vs pH in the range from 9.5 to about 11 which covers low to high contrast developers.

    This, I guess, led me to the conclusion that a single number is simply insufficient. The tables or graphs can be seen to change slope for different developers, and I posted a sample table in another thread. Given a "starting point" can waste a lot of film, but given the table can just about lead you to the right value immediately.

    In addition, please note that on the time (X) axis, the values are logarithmic which means that the data is non-linear and this is certainly not shown in the use of single values, nor can it be shown.

    PE
     
  6. gainer

    gainer Subscriber

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    I should point out that Pyrocat HD does not contain hydroquinone. The two agents it uses are pyrocatechin, AKA catechol, and Phenidone. Hydroquinone is 1,4 dihydroxybenzene and catechol is 1,2 dihydroxybenzene. They are both capable of being used as staining developers, each with its own color.

    One would expect a Phenidone-Quinol developer and a Phenidone-Catechol developer, all else being the same, to have similar temperature coefficients, though expectations in such matters are not always met.
     
  7. Lee L

    Lee L Member

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    A quick look at Kodak tech pub J-78 for D-76 shows the slopes of temp vs development time varying by a factor of 1.7 across 6 films at 1:1 dilution. With that much variation using the same developer and dilution, I don't see how you can generalize usefully using the factors you quote across different developer formulations or different films.

    Better to go with the charts as PE and others have said.

    Lee
     
  8. edtbjon

    edtbjon Member

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    Hmm, to clarify a bit more...
    I didn't open this issue up to bang a few numbers into your heads, rather to start a discussion. As PE have pointed out in this thread and certainly many others in the (now found) older thread on the subject, there are many factors which affect the dev.time when changing the temperature. All of that info seems to be covered in the thread linked in my post above.
    Understanding the subject a (very tiny) bit better, it certainly adds to the concept of keeping it down to as few variables as possible. I.e. try to standarize on one developer and one film, until you really know what the combination is capable of. Then maybe one more film with the same developer. The only good thing about the "recession" of analogue photography is that there arn't as many temptations out there as there used to be.

    //Björn
     
  9. gainer

    gainer Subscriber

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    A rule of thumb that I learned in Physical Chemistry is that the rate of a reaction doubles with 10 C degrees increase of temperature. This curve plots as a straight line on semilog graph paper. Over short temperature range, this rule is good enough for most of the developers we use.
     
  10. Tom Stanworth

    Tom Stanworth Member

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    i.e. a 10% increase in reaction speed for every 1 deg C increase. i use this rule of thumb for dev times on the plus and minus side of 20 degs C. However, I have generally found that when i have large changes, such as developing at 17 degs or at 25degs C, I reduce the amount of change somewhat. I generally shoot rollfilm shot in a wide variety of conditions, so add or subtract a little depending on my perception of the contrast of the scene. Never had real problems. In the summer my water temperature is about 23-25 degs and in winter 16-17, so I have to try to stabilise the room temperature for a little bit before i develop to bring water containers as close to 20 degs C as I can. A few degs C either way and the 10% rule gets me nice and close.
     
  11. Photo Engineer

    Photo Engineer Subscriber

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    That rule of thumb can work vaguely, but only for ONE developer. If you have a group of them, you can't apply it across the group, nor can you apply it across films. Oh well. I'm ready to give up on this subject.

    PE
     
  12. Kirk Keyes

    Kirk Keyes Member

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    See "Arrhenius Equation".
     
  13. gainer

    gainer Subscriber

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    I did.

    There was nothing vaguely vague about any of Dr. Collett's rules of thumb. There are two constants in the equation usually applied to film and developer, which is presented along with a simple form of the Arrhenius equation. They allow for different slope and intercept on semilog paper graphs. Over any reasonable range of temperatures I would allow in my darkroom, the simple equation works very well. If you have only one experimental point, you can plot another one at 10 C higher and half as long, or 10 C lower and twice as long and draw the line between those points to get a very good guess at your next experiment.
     
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  15. Photo Engineer

    Photo Engineer Subscriber

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    Patrick;

    After 15 years of doing the "real" work on this, I find that the Arrhenius equation is only a vague approximation due to a number of factors. The film, the developers, the ratio, the pH, the temperature ad nauseum....

    All of these tend to distort the original assumption. And, they just don't always work. I have applied (or tried to) over 32 years and found exceptions in every case. Sorry.

    PE
     
  16. Tom Stanworth

    Tom Stanworth Member

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    PE,

    I am sure you are right! However, I think another important factor here is how accurate people need to be, esp with the use of VC materials. If at 20 degs C my correct dev time is 10 mins and I use 11 at 19 degs (whereas the correct time should in fact be 10.75 or 11.5, it is neither here nor there for VC use.

    Can you explain whether making a 10% change for each degree could be more wrong than making no correction. I know this sounds daft, but say at 20 degs C the time should be 10 mins and at 22 degs C I use 8 (whereas the correct factor dictates it should be 9.1, I have made a bigger error by applying correction than none at all.

    I guess one needs to use teh provided slopes unless one is using a bespoke developer or one where such things are not supplied, such as pyrocat.
     
  17. Photo Engineer

    Photo Engineer Subscriber

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    Tom;

    The OP was comparing developer A to developer B and referred to film. If you use one developer and one film, you may see what you refer to as temperature varies.

    Consider the attached chart which I am reposting. Note that the slopes of the developers vary greatly and some are even the reverse of others.

    This may completely upset things if you move across this set of developers. Note the DK-50 in particular, and how it has a vastly different slope than the other developers.

    PE
     

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  18. Kirk Keyes

    Kirk Keyes Member

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    It's interesting that some people are so enthralled with items like the Zone VI compensating timer. Obviously, it does not know what developer is being used, and I assumed it used the Arrhenius Equation (I like to say that as I know how to spell "Arrhenius"...) to make it's time corrections. There's even a newer version of this type of timer being made that is software along with a stand-alone USB temp probe. Kind of funny.
     
  19. drazak

    drazak Member

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    Well, looking at this from a chemistry standpoint, there are a lot of factors that affect rate, however, for each developer, you could conduct a densiometer study and determine two points on a graph of rate of development (measured indirectly as a gamma, in this case) vs. temperature, and then extrapolate other points on the graph from it, you can also get a lot of other chemistry data from this graph (you'll have to excuse me, I can't remember all of the data that this graph can help you with). After the AP's this year, I'm planning on doing a study on developing agents and their associated rate laws. I'll be happy to let you guys know how that all works out when I get there after the second week of may!

    Ben
     
  20. gainer

    gainer Subscriber

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    According to "The Theory of the Photographic Process", Third edition), the temperature dependence of the rate of development can be expressed roughly in terms of a coefficient, called k, which is the ratio of the rate at a particular temperature to the rate at a temperature ten degrees higher on the Kelvin scale or 18 degrees higher on the Fahrenheit scale. Among the factors affecting k is pH. It was not noted in the reference, but a plot of log(k) vs pH is for practical purposes a straight line between pH values of 7.8 and 10 and values of log(k) from .477 to .362. This region of linearity includes various compositions of Metol, Metol and hydroquinone, and catechol.

    Here is a table of the data presented in the reference.
    Developer Kbr pH k log(k)
    Sease III 1.0 7.8 3.0 0.477
    Metol without alkali 0 8.0 2.9 0.462
    D-76 0 8.4 2.8 0.447
    Gevaert 206 (MQ) 0 8.9 2.6 0.415
    Agfa 14a 0.5 9.75 2.4 0.380
    Metol-Na2CO3 0.5 9.85 2.3 0.352

    The attached graph shows k vs. pH on semilog paper.

    We can calculate the k for line C on the graph PE sent to be 2.2. D-19 is on that line. If the log(k) vs pH relationship stands, the pH of D-19 should be about 10.4.
     
  21. gainer

    gainer Subscriber

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    Developer temperature, time

    As usual, the digital world has thwarted my effort to show you a picture. Try, try again.
     

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  22. gainer

    gainer Subscriber

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    It seems that if the Zone 6 compensating timer had included a pH meter somewhere in the loop, it might stand a better chance of satisfying Kirk.
     
  23. drazak

    drazak Member

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    I've spoken with PE on phone and via email about doing a few experiments having to do with determining the effects of temperature and time on film results, I figure that I'll use a couple different types of film, as to make sure the results between them are fairly consistent. From the graph that PE had posted, it seems that DK50 and D76 have the most different lines, so I will use each developer at different temperatures and times with a a step wedge of known densities (IE. a stoufers step wedge). I will measure results with a densitometer and post them on here, if people are interested, I'll even repeat the experiment uses developers with differing developing agents, IE. pyro and paraminophonel and glycin developers.

    Ben
     
  24. gainer

    gainer Subscriber

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    Be sure to record the pH of the working solution of the developer. That is something we rarely see in descriptions of developer experiments.
     
  25. drazak

    drazak Member

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    Of course, that's all part of good note taking, heh. Most of the pH's can be calculated though, as well as determined empirically.

    Ben
     
  26. Tom Stanworth

    Tom Stanworth Member

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    I think I will just try to develop at 20 degs C every time, or at least darned cloe LOL! This is waaaay too complicated for me.

    I am quite partial to Xtol mixed with rodinal at the moment so I dont suppose I am going to find any published figures for that! I know some love to be super accurate, but I have found a bit extra here, or a touch too little there has no real impact on my ability to make a really satisfying print. still, it is nice to be able to get things right, consistent etc.

    A simple question (I hope): By compensating by +/- 10% for every degree either side of 20, is this too much or too little compensation for most developers?