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Alan Johnson
02-21-2012, 08:43 PM
PE,

I agree one should not use the same spoon calibration for sulfite from 3 different sources.

Here are the weights of 1 Asda teaspoon of sodium sulfite anhydrous from the same batch,in grams:
6.7, 6.8, 6.6, 6.7, 6.7, 6.7, 6.7, 6.6, 6.6, 6.7, =6.68 +0.12/ -0.08 an error of less than 2% if each spoon is first calibrated to each source.

One could use a spoon to measure the sodium sulfite to add to say 500ml working solution along with the 50x concentrate from a 10ml syringe.Using say 24.5g or 25.5g sulfite isn't going to make a detectable difference to the negatives.

But as you say,don't use the same spoon calibration for sulfite from different sources.
Nobody uses Crawley's FX-55 developer AFAIK,probably because it calls for some ingredient to be weighed out each time before use.

Photo Engineer
02-21-2012, 11:01 PM
Well, I never uses spoons except to dip out chemicals onto my scale or balance!

Besides, I am still thinking SKYPE.

PE

albada
02-21-2012, 11:28 PM
Well, I never uses spoons except to dip out chemicals onto my scale or balance!
Besides, I am still thinking SKYPE.
PE

The topic here is spoons, so SKYPE must stand for:

Spoons Kill Your Photographic EmulsionStupid joke, but you'll never forget it. :)

Mark Overton

Photo Engineer
02-22-2012, 09:26 AM
At my age you would be surprised how fast you can forget things!

:D

PE

nworth
02-22-2012, 04:34 PM
As for teaspoon measures, I generally side with PE, especially with developers. But it really depends on how much accuracy is needed. There are plenty of cases where a -50/+100 percent error is acceptable.

albada
02-22-2012, 08:32 PM
Why does 1+1 dilution (with XTOL anyway) increase grain compared to 1+0?

Ron has said that longer dev-times can improve image-quality, but dilution (with longer time) makes it slightly worse.
I've also found that lowering pH (which means boosting time) improves image-quality to a point.

With a concentrate, there's a trade-off between concentration and dev-time, and the longer time that's associated with higher concentration means a little more grain (and I'm wondering why). I'm recovering that loss of quality by dropping pH, boosting time even more. As PE said, "What's the hurry?"

Mark Overton

Photo Engineer
02-22-2012, 11:14 PM
It depends also on pH. A well buffered system does not go down in pH. There are so many factors that it is difficult to say.

PE

Rudeofus
02-23-2012, 02:50 AM
Why does 1+1 dilution (with XTOL anyway) increase grain compared to 1+0?
Because you dilute not only the dev agent but also the solvent? You recently posted recipe doesn't do that. If you want to investigate the influence of one parameter on the outcome of your experiment, it's imperative that you really change only this one parameter or the comparison won't tell you much


With a concentrate, there's a trade-off between concentration and dev-time, and the longer time that's associated with higher concentration means a little more grain (and I'm wondering why). I'm recovering that loss of quality by dropping pH, boosting time even more. As PE said, "What's the hurry?"

As mentioned before, we/you won't be able to beat Xtol on all terms, but you/we have a reasonable chance to achieve better image quality if we relax some of the design rules which apply to commercial devs. Short dev time is one of them, sufficient capacity (250ml enough for 36 exp. 135 film) would be one, long shelf life could be a third. With your low pH experiments we might once create a dev which only works reliably if we measure and adjust the pH before every run.

Ian Grant
02-23-2012, 04:28 AM
Why does 1+1 dilution (with XTOL anyway) increase grain compared to 1+0?


As Rudeolfus says the dilution cuts the Sulphite level which is the key to grain control in many developers like D23, D76/ID-11 etc as well as Xtol.

In practice the 1+3 dilution gives the worst grain and Kodak have dropped that dilution from their datasheets for both Xtol and D76 in recent years. However with dilution there's a trade off of increased grain compared to increased sharpness and acutance and a good balance point is a dilution of 1+2.

The critical level of Suphite appears to be around the 25-30 g/litre but this may vary with films but my own experience with both D76/ID-11 and Xtol and Fp4 and Tmax 100 is that grain control with both developers is good at 1+2 dilution but for optimum results in terms of fine grain, acutance and sharpness replenished Xtol is better still.

Ian

albada
02-23-2012, 06:46 PM
Because you dilute not only the dev agent but also the solvent?

Hmmmm... And Ian Grant also suggests this.

Diluting 1+1 cuts sulfite in half, but dev-time doesn't double, and even if it did, solvent-effect isn't linear. So there's less solvent-effect, and that would make sense why 1+1 would worsen grain.
Thanks for pointing this out.

Different question:

How do folks feel about measuring a concentrate by weight instead of by volume? I love my electronic gram scale, but would most users of a developer want to buy one? Or would most folks prefer to measure by volume using a graduate? That's fine for concentrate, but it means greater error when measuring sulfite. Do you think most non-home-brewers would be put-off by measuring by weight?
BTW, potassium sulfite concentrate makes it easy to measure everything by volume. It's a pity that it's hard to obtain in much of the world.

Mark Overton

Rudeofus
02-24-2012, 02:23 AM
How do folks feel about measuring a concentrate by weight instead of by volume? I love my electronic gram scale, but would most users of a developer want to buy one? Or would most folks prefer to measure by volume using a graduate? That's fine for concentrate, but it means greater error when measuring sulfite. Do you think most non-home-brewers would be put-off by measuring by weight?
BTW, potassium sulfite concentrate makes it easy to measure everything by volume. It's a pity that it's hard to obtain in much of the world.

Under all normal circumstances measuring by weight is the thing to do, after all we usually don't deal with solid blocks of material but with powders and flakes, where density may vary, and moles are directly tied to weight, not volume. The only big exception are solutions, because dilution is commonly measured by moles/liter or kg/liter. In this case the volume of the liquid, aqueous or not, is directly proportional to the moles of agent and therefore the most easy to use measure of total agent amount. If you go through the effort to measure the density of such a solution, you can easily convert between volume and weight of such a solution.

It is clear that a 2% solution of X contains twice as many grams or moles of X per volume than a 1% solution. In terms of weight, there is no such easy relationship, since volume of a liquid may rise or shrink if you dissolve a substance. There is no simple rule to determine the density of a solution!

Personally, I wouldn't worry much about the requirement to get a scale which measures 0.01g. You are right on track towards very critical developers where tiny deviations in some components could trigger big differences in results. You have noticed yourself that you do no longer write about pH of 9 or 10 but about 7.95 and 7.92. My recommendation to everyone trying your latest recipes would be: plunk down money for a moderately precise scale, it's not going to break the bank and ensures that you get results similar to Mark. If you want to experiment on your own, go get a decent pH meter, too, or your results may vary to much to be repeatable and useful to others.

Ian Grant
02-24-2012, 04:08 AM
Hmmmm... And Ian Grant also suggests this.

Diluting 1+1 cuts sulfite in half, but dev-time doesn't double, and even if it did, solvent-effect isn't linear. So there's less solvent-effect, and that would make sense why 1+1 would worsen grain.
Thanks for pointing this out.



When I used D76 and later Xtol dilute my own experiences were that any slight increase in grain at 1+1 & 1+2 was out weighed by the overall increase in sharpness and acutance. It's that balance of grain, sharpness and acutance along with tonality are important, and we don't all want the same balance.

When looking at the sulphite concentration it has to be remembered that dropping the level in a developer like D76/ID-11 fro 100g/litre to 80g/litre results in an increase in developer activity but no increase in grain, Agfa 44 (Agfa Ansco/Gaf 17) and Adox Borax MQ both give less speed loss, better sharpness and slightly finer grain, which leads to smotther tones.

The ratio of Hydroquinone to Metol also plays a part, in D76 it's 2.5:1, Adox Borax MQ and Agfa 17 it's 2:1 while in the oldest Fine grain developer I've come across it's 1:1. Welington & Ward's Borax MQ developer (for delicate Fine Grain negatives) pre-dates the first Fine Grain developer published by Kodak by a few years - Kodak eveolved this formula into DK50.

Ian

albada
02-24-2012, 04:31 PM
Yet another question for the chemists:
Among PG-soluable acids and bases, which acid-base pair gives the most buffering per gram of total weight?

In my present version of the concentrate, I have 7 grams/liter to allot to an acid and base to (1) set the pH to 8.00, and (2) provide as much buffering as possible. I can do things like:
6.5 grams of sodium metaborate plus 0.5 grams of citric acid, or
3.5 grams of sodium metaborate plus 3.5 grams of boric acid, or
6.5 grams of TEA plus 0.5 grams of citric acid, or other possibilities.
BTW, the numbers above are rough guesses. And they assume that ascorbic acid and sulfite are/will be added.

It's easy to adjust pH, but I'm wondering what combo maximizes the buffering, especially between the first two possibilities above.
Thanks!

Ian: Thanks for the reminder about trade-offs between fine grain and acutance. Also, I want to explore Metol, Hydroquinone and PPD, but there's only so much time...

Mark Overton

Photo Engineer
02-24-2012, 05:58 PM
The answer to your question varies with pH.

PE

Rudeofus
02-24-2012, 07:13 PM
6.5 grams of sodium metaborate plus 0.5 grams of citric acid, or
3.5 grams of sodium metaborate plus 3.5 grams of boric acid, or
6.5 grams of TEA plus 0.5 grams of citric acid, or other possibilities.
BTW, the numbers above are rough guesses. And they assume that ascorbic acid and sulfite are/will be added.

At the start of this thread you posted a link to a pH calculator, maybe now's the time to put it to use. It's easy to calculate the moles from weight so you have the concentration. pKa and pKb can be found online, especially for the substances you listed here. Fine tune the mix to get the pH you need, then (virtually) add HCl or NaOH to your setup and see how much the calculated pH level changes.



It's easy to adjust pH, but I'm wondering what combo maximizes the buffering, especially between the first two possibilities above.

If it's easy to adjust the pH of a buffer, then it's a poor buffer :p

Kirk Keyes
02-25-2012, 12:45 AM
I have a feeling he means it's easy to make a buffer for a particular pH...

albada
02-25-2012, 01:23 AM
I have a feeling he means it's easy to make a buffer for a particular pH...

That's correct. It's easy to add base or alkali while watching the pH-meter until a target-pH is reached. But it's hard (for me) to determine which choice of chemicals yields the strongest buffer.

Ron: My target pH is 8.0. Sorry I forgot that detail. Forgetting details is something I'm good at; I call it one of my "core competencies". :(

It occurred to me during my half-hour walk today how to answer my own question: Mix up the chemicals, and measure pH-shift resulting from adding a little base or alkali. Select the brew that gives the smallest shift. Problem solved. This evening I measured the metaborate/boric-acid combo. Tomorrow will be the metaborate/citric-acid combo.

BTW, I discovered a quick way to dissolve boric acid: While mixing the chemicals, heat a little water in a separate beaker on the side. When it's up to 60-70C, add the boric acid. It dissolves within a minute. Then pour that beaker into the brew.

Mark Overton

Rudeofus
02-25-2012, 03:58 AM
That's correct. It's easy to add base or alkali while watching the pH-meter until a target-pH is reached. But it's hard (for me) to determine which choice of chemicals yields the strongest buffer.
Sorry, but I was right. You can change a buffer to any pH value by adding copious amounts of KOH or HCl, but outside its ideal range it won't buffer well. There are many docments to be found online which show the borax/boric acid buffer combo to be exactly where you want it: almost symmetrically around a pH value of 8.


Ron: My target pH is 8.0. Sorry I forgot that detail. Forgetting details is something I'm good at; I call it one of my "core competencies". :(

The borax/boric acid buffer is frequently used in devs, so it is well understood and doesn't interfere. Since pH of 8 lies in the center of its range, I'd suggest you use it. Be careful with Borax (http://www.borax.com/pdfs/dist/Profile_Borax_Decahydrate.pdf), it dissolves poorly at 20C. Sodium metaborate is easier to dissolve but its pH is too high.


It occurred to me during my half-hour walk today how to answer my own question: Mix up the chemicals, and measure pH-shift resulting from adding a little base or alkali. Select the brew that gives the smallest shift. Problem solved. This evening I measured the metaborate/boric-acid combo. Tomorrow will be the metaborate/citric-acid combo.
Look at borax/boric acid, borax is much cheaper than metaborate and you need less boric acid to reach the pH you want. Don't waste your time&money mixing endless rows of combos, use that online pH calculator you posted about. You may well find out that one buffer combo works slightly better than the other but that the difference is not worth the trouble at this stage. If buffering is really an issue, just use more soup with the same amount of film!

Photo Engineer
02-25-2012, 11:24 AM
I would have to say that Boric Acid / Borax is one of the best choices with the rations balanced to get the target pH and the total quantity being above 20 g/l and not more than 3/4 saturation for a start. Another combination is Carbonate / Bicarbonate.

PE

Rudeofus
02-25-2012, 11:53 AM
I would have to say that Boric Acid / Borax is one of the best choices with the rations balanced to get the target pH and the total quantity being above 20 g/l and not more than 3/4 saturation for a start. Another combination is Carbonate / Bicarbonate.

If you use borax/boric acid, plan ahead, borax just doesn't want to dissolve fast, even at 40C :( And I mean many hours, not minutes ...

Carbonate/bicarbonate is described here (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1258214/pdf/biochemj00962-0041.pdf), but it is claimed that only pH values between 9 and 11 can be reached. For pH of 8 and good buffering something more acidic must be used. How about monosodium phosphate/trisodium phosphate (http://home.fuse.net/clymer/buffers/phos.html)? Both components are much more water soluble than borax.