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  1. #1

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    Progress on XTOL-concentrate

    Although I've been quiet for weeks, I've still been busy trying to create a concentrated version of XTOL that will keep for years. I think I'm close. Below is the graph of true XTOL versus my test-dev (TMY2, 6.5 min at 20C):
    Click image for larger version. 

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    As you can see, the two curves are so close that they appear to be one curve in the thumbnail. And careful exam in my 22X loupes shows the grain is the same too. Here's the formula:

    Propylene glycol .................... 24 ml
    Sodium metaborate 4 mol ..... 6.7 g
    Ascorbic acid ......................... 8.5 g
    DimezoneS/Phenidone .......... 0.2 / 0.105 g
    Propylene glycol to ................ 33.3 ml (final volume)
    (heat to 90C to dissolve everything and drive out the water in the metaborate)
    To make one litre of developer, mix 33.3 ml of concentrate into water containing 90 grams of sodium sulfite. That's 1+29 dilution.

    So far, I've tested this by mixing the ingredients directly into water; I haven't actually made any concentrate yet. That's the next step.

    Chemists will be interested in the latest weird problem I had:
    Adding the propylene glycol to that developer drops the pH by .07 and raises the temperature by 1 degree C. So it appears to react with something. Adding PG to XTOL does not change its pH, and the only thing my dev has that XTOL lacks is ascorbic acid, so I'm guessing that AA reacts with PG. The dev works fine anyway, but I had to remove a little acid and add a little alkali to correct the pH. PG is not as inert as I thought. Do the chemists here have any idea what's happening?

    Mark Overton

  2. #2

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    Hi Mark, I can't remember - why didn't you use sodium isoascorbate in your formula? Sorry if this was addressed in the previous thread but I didn't have the time to re-read everything. Nice to see you've continued with this project.

    Michael

  3. #3
    yeknom02's Avatar
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    Speaking of the older thread, can someone link to it? I'd be interested to read what's been going on until now.
    "When the going gets weird, the weird turn pro." - HST
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  4. #4

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    Responding to both questions:

    @Michael R 1974: I used ascorbic acid instead of isoascorbate because ascorbic acid is easy to obtain. You can even buy it at health food stores, whereas isoascorbate was not even sold by Photo Formulary the last time I checked.

    @yeknom02: Here's the link to the long DS-10 thread:
    http://www.apug.org/forums/archive/i...p/t-98430.html
    This is basically all my questions, answers and discussion about developers and my unexpected experiences with them as I was learning about the topic. Home-brewing developers is full of surprises. Several knowledgeable people contributed much good information in that thread, so it's worth reading.

    Mark Overton

  5. #5

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    By the way, here's a trick I've been using to develop short test-strips uniformly with a small amount of developer. I hold a strip to the bottom of a stainless steel tank using hobby-magnets. Here's a photo of a strip after fixing:
    Click image for larger version. 

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    Be sure the emulsion is facing up! The magnets don't rust, so they should not cause iron-contamination. But they stick poorly to the tank, so there are four more magnets under the bottom of the tank to hold those inside-magnets in place (8 magnets total). I develop in a water-bath to hold temperature to within .1 or perhaps .2 degree C, agitating with inversions. I use 100 ml of developer, but 50 ml would probably work also. I'm getting good consistency with this set-up, so I figured I'd share it with other experimenters.

    Mark Overton
    Last edited by albada; 07-09-2012 at 01:17 AM. Click to view previous post history.

  6. #6
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    Quote Originally Posted by albada View Post
    Chemists will be interested in the latest weird problem I had:
    Adding the propylene glycol to that developer drops the pH by .07 and raises the temperature by 1 degree C. So it appears to react with something.
    Propylene glycol is a weak acid which may lower your pH to some extent. A rise temperature may or may not indicate a chemical reaction in the most narrow sense, think about dissolving sodium thiosulfate in water.
    Quote Originally Posted by albada View Post
    Adding PG to XTOL does not change its pH, and the only thing my dev has that XTOL lacks is ascorbic acid, so I'm guessing that AA reacts with PG.
    XTOL may be much more buffered than your dilute soup. Which brings up an interesting point: Can you see a difference in edge definition between XTOL and your soup?

    @Michael: I have no idea why people would recommend sodium ascorbate instead of ascorbic acid, when the latter one is so easy to obtain from any third rate pharmacy.
    Trying to be the best of whatever I am, even if what I am is no good.

  7. #7

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    PG may also change dissociation:
    http://www.chemvistasolutions.org/pr...surements.html
    What is the pH of this developer and the development time in the dilute solution?

  8. #8

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    Quote Originally Posted by Alan Johnson View Post
    PG may also change dissociation:
    http://www.chemvistasolutions.org/pr...surements.html
    What is the pH of this developer and the development time in the dilute solution?
    @Rudeofus: The buffering should be similar to or even better than XTOL, because the AA will improve buffering some and I'm using more metaborate. However, I wrongly thought that PG was neutral. I gotta check these things in the CRC Handbook.

    @Alan: The pH (with the PG mixed in) is 8.33, which is .04 higher than the 8.29 I measured for XTOL. The dev-times are intended to be the same as XTOL. I used 6.5 min @ 20C for TMY2. That article about differing dissociation-constants is interesting. Thanks for pointing that out.

    Mark Overton

  9. #9
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    Quote Originally Posted by albada View Post
    @Rudeofus: The buffering should be similar to or even better than XTOL, because the AA will improve buffering some and I'm using more metaborate.
    I'm not sure how you arrive at this conclusion. Xtol uses about 100g powder per 1l of regular soup, while your soup uses about 15 g/l, so even diluted Xtol has more powder per liter. I don't know the composition of Xtol but would assume that some of that amount of powder helps buffering. AA has pKa values of 4.1 and 11.8, which will not help buffering around pH of 8.3.
    Trying to be the best of whatever I am, even if what I am is no good.

  10. #10
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    Adding plain alcohol to water will raise the temperature. So, PG and water does not surprise me.

    Good work Mark. I am waiting to see the sharpness and grain. We can see the grain from an enlarged scan of your step wedge.

    PE

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