Rodinal with Ascorbate - what am I doing wrong???greenspun.com : LUSENET : B&W Photo - Film & Processing : One Thread
I've been playing around with a few film and developer combinations to try to settle on a 50-100 speed combination that provides high sharpness, reasonably fine grain and nice gradation. I'm playing around with Acros and TMX in Xtol and Rodinal, and after setting an Xtol and 1:50 Rodinal baselines, I processing a test strip of TMX in Rodinal with some added ascorbate.
As I don't have a local source of Sodium Ascorbate, for my first test I mixed developer using 1/2 tsp of ascorbic acid (Vit C), 1/4 tsp of baking soda, 500ml of water (lots of fizzing when the soda was added to the ascorbic acid/water mix) with 10ml of Rodinal (1:50). I developed for 8 minutes and got an image - thin, but still printable at EI 50.
To boost the density, for the next test I doubled the ascorbate proportion by using 1 tsp ascorbic acid with 1/2 tsp baking soda an increased the dev time to 10 mintues - the result, a very, very faint image that was completely unprintable. Thinking that the ascorbic acid may not have been fully neutralized by the baking soda, I tried again by adding soda until the ascorbic acid/water mix stopped fizzing ended up being about 1 tsp ascorbic acid, .6 tsp soda. The result - no image at all, no edge markings, blank film base.
I can't for the life of me figure out what I'm messing up. I thought that I was following Patrick Gainer's suggestions regarding teaspoon mixing (where he suggests consistency is more important than absolute accuracy), but it appears that my ascorbate addition is neutralizing the Rodinal.
From the positive feedback I've read from others, I don't want to give up but don't know what I'm doing wrong. Any suggestions?
-- David R. Williams (email@example.com), May 06, 2002
If you don't want to minimize the steps and get the good result, I recommend to buy sodium ascorbate. If you don't buy it, use hydroxide to neutralize. Or even simpler, switch to Ilfosol-S. If you are looking for a match for TMX, also try Microphen 1+1 or 1+3.
I do not understand why bicarbonate is recommended to neutralize ascorbic acid. Unless you want to make a very low pH developer this just makes things difficult. Here's a little review from freshman chemistry. Ascorbic acid's pKa is about 6, and that of bicarbonate is about 7.6. Remember if pH is near pKa, that compound is only about 50% dissociated. If you mix similar molar quantity of these, they'll result in somewhere near neutral pH region, meaning that some of each are dissociated, some of each are not dissociated. It doesn't quite look like a textbook buffer, but acts as a buffer. There is even more thing involved in this complicated buffer that affects its pH. The gas you saw is carbon dioxide from bicarbonate. Solubility of CO2 in water (to form carbonic acid) decreases as pH goes down, so when carbonic acid sees ascorbic acid, it gives up the gas. This removal of carbonic acid moves around the bicarbonate <--> carbonic acid equilibrium. This decreases titratable base, as well as the proton provided from the ascorbic acid. Yet there are some undissociated acid and base. What it means is that this ascorbic acid and bicarbonate mixture will pull the pH down from Rodinal's normal operating pH. Adding more of this mixture would pull the pH even farther, and Rodinal would cease to function at such a low pH.
Ascorbic acid can be used as a part of the buffering system if the developer is appropriately formulated. I generally prefer this approach for low pH developers. However, Rodinal is poorly buffered high pH formula that is rather intolerant of acidic disturbance. To Rodinal, even bicarbonate looks like an acid.
(ascorbic acid is diprotic but the second dissociation is not of interest unless you are looking at very high pH. even so, the theory is the same)
-- Ryuji Suzuki (firstname.lastname@example.org), May 07, 2002.
Wow, Ryuji must have payed a whole lot more attention in freshman chemistry than I did.
I hope that this is not straying too far, I'm staying with the ascorbic acid line. I don't have any metol around, so I am going to use just enough D-76 powder to get the equivalent amount of Metol. This will also give me about 10 grams/liter of sulphite (notice the spelling, I took freshman chemistry a long while before Ryuji). This amount of Sulphite should be about equivalent to what Rodinal has. I planned to mix the ascorbic acid and the D-76 together for part A. Do you see any problem with this?
This will also give me about 0.5 g/liter of hydroquinone in the part A stock solution. I am assuming that this will give the metol a little boost, but not much. I was going to start with D-76 straight times. Does this sound about right for a starting point for testing? I'm using FP4 (Arista 125) 4x5.
Thanks to all for comments. This is the first time in 30 years that I've processed film and I really looking forward to getting back in.
-- Mike Bell (email@example.com), May 07, 2002.
I know you did not ask this question, but..... I highly recommend you try both films in Rodinol 1:100 for 20 minutes @ 70 degrees with two minute agitation at the beginning and then five seconds every minute. I also use the combination with Neopan 400 and love the results. You may want to lower your EI to about 80.
-- Christian Harkness (firstname.lastname@example.org), May 07, 2002.
David, Ryuji's advice is right on. If you must use ascorbic acid, then use sodium hydroxide to neutralize it. My experiments using baking soda resulted in the same dismal negatives you got. Hydroxide with ascorbic acid will work, but I too strongly urge you to get sodium ascorbate. Most healthfood sources stock sodium ascorbate, but if you don't have it available locally, Now Foods, among many other sources, sells it via the internet.
Also, considering the films you are using, you might want to try a catechol based developer such as Pyrocat-HD. (The formula is available at Ed Buffalo's site, unblinkingeye.com.) Acros and TMX respond very nicely in catechol formulas, with negatives exhibiting very high sharpness, tight grain and excellent tonality.
-- Ted Kaufman (email@example.com), May 07, 2002.
I don't know what is your intention, but if you are trying to make Gainer's metol-ascorbate-carbonate developer, avoid that substitution for best result. Hydroquinone will be 50% dissociated around pH of 10, and that's about the pH carbonate will get. However, I suggest experimenting with D-76 (assuming the published formula, ID-11 more likely a better candidate here) and 5g ascorbic acid, 10 to 12g borax added to it, and dilute 1+1 to 1+4 from there. You can do similar thing with D-76R which has extra borax already in the package so you can add about 10g ascorbic acid per liter of D-76R and then dilute 1+3 or more for use. I haven't tried these myself because I have metol at hand, but they are similar to what I use - ascorbate version of D-76.
I think British people still spell sulphite... and I was already doing darkroom work when I took series of chemistry classes :-)
-- Ryuji Suzuki (firstname.lastname@example.org), May 07, 2002.
Ryuji, I think sometimes that your theories keep you from having a lot of fun. I seem to remember that the pH of ascorbic acid solution is about 3. What happens when you use bicarbonate to neutralize it depends on how much water you dissolve it in and how cold it is. The CO2 that makes the fizz will not be there if you use enough water. This is not good. Carbonic acid is weak enough so that we can drink it, but one molecule of it still neutralizes 2 molecules of NaOH. I get good results when I mix the ascorbic acid powder and baking soda in a very small alount of warm water. This mixture is not harmful, so you can taste it with the tip of your tongue to see if it still has any sour or tangy taste. Sodium ascorbate is very near neutral pH in solutions as high as 10%. The amount you put in Rodinal is .2 % of the working solution. If you increase the amount of baking soda beyond that needed for neutralizing the ascorbic acid, you begin to form a hydroxide-bicarbonate buffer solution. The 8 grams or so swamped the hydroxide in the Rodinal, which is actually very small in a 2% Rodinal solution. Now you have a developer with sparse amounts of developing agents and a low pH. I am not trying to promote ascorbatized Rodinal. It does give finer grain than plain Rodinal while keeping some of the other characteristics, but I would and do use a little metol or phenidone in place of it most of the time.
-- Patrick A. Gainer (email@example.com), May 08, 2002.
Everyone should review chemistry for fun! :-)
Patrick, I never said anything about pH of ascorbic acid. Indeed, the pH depends on the concentration. pKa is simply a negative log of the dissociation constant, and is independent of concentration. There are a lot of misconceptions about what acids are strong and what acids are weak. Without an intention to fix the misconception, I simply state some examples. Citric acid is strong in the sense its pKa and the pH are very small (pH at a typical concentration) and most many of which will release proton when dissolved in water. Yet we can drink it in fruit juice with no harm. Ascorbic acid is weaker than that. Boric acid is much weaker, but you shouldn't drink any appreciable amount.
Tongue tip is very insensitive to bitterness. Although there are classic and recent data that are somewhat controversial to see together, if you stimulate only the tongue tip with some solution, it is a good receptor for sourness but not for bitterness. This tells us that even if it doesn't taste bitter, it does not mean you overdosed bicarbonate. There can be excess bicarbonate without giving you bitter sensation if you only stimulated the anterior portion of the tongue. (You can ask a neuroscientist, coffee cupper, or wine taster :-)
The fact you stated - two moles of NaOH neutralize one mole of carbonic acid is because NaOH is a strong acid and 100% dissociated, and the solubility of CO2(g) only increases as the pH increases. This does not extend to other cases we are talking about.
The developing ability of each developing agent must be evaluated at the targeted pH. It's not just because the concentration of free OH- changes, but also because dissociation of those developing agents change with pH.
Regarding Vitamin C developers developed by Gainer, I think ones that are most useful are phenidone version adjusted for moderate pH, especially if supplemented with a small bit of bromide. Metol versions would benefit from presence of some sulfite (10-60g/liter).
There have been a few additives proposed for Rodinal users. I think some of their effects are due to lowered pH, but this is hard to prove because once you fix the pH of Rodinal it is very different from Rodinal. Ascorbates are likely very different because it is capable of regenerating oxidised developing agents (without silver halide solvent effect) but then one might ask what if I mix my ROdinal with extra p-aminophenol hydrochloride adjusted for suitable pH?
I agree with what Gainer's vitamin C formula try to exploit: because the immediate oxidation product of vitamin C (DHA) is colorless, one might not need sulfite, if ascorbate is abundant and the solution is mixed immediately before use. It somewhat helps cost and environment in some way. I'm not a big fan of Rodinal (doesn't mean I don't like it -- I like something else better) and I like straight Vitamin C formulae better.
However, cheap and good can be bad, like the wine I found last week -- I've been drinking too much just because it's too good and cheap. Hope you figured from my redundant writing and grammatical errors :-)
-- Ryuji Suzuki (rsuzukI@rs.cncdsl.com), May 08, 2002.
I forgot one thing to say, anticipating Pete Andrews favourite comment "photographic chemistry is a black art." I AGREE! It's probably only just a bit more predictable than making a good wine and good stout... (and I read a lot more about pyrocatechin about publications on beverages than photography!)
-- Ryuji Suzuki (firstname.lastname@example.org), May 08, 2002.
I was not concerned about bitterness. I wanted some easy way to make reasonably sure that all the CO2 had escaped after the proper proportions of ascorbic acid and sodium bicarbonate had been mixed. That is the biggest source of disappointment that has been reported to me by some who tried ascorbic acid with Rodinal. Even though they used the proper amount of bicarb to come close enough for government work, leaving the CO2 in solution kept the pH too low. I seem to remember that the manufacturers of sodium ascorbate use bicarbonate and ascorbic acid. I am not much of a wine connoiseur. Some friends of mine have a vineyard and winery close by. I have been invited to a wine tasting on May 10. If I make it, I will keep in mind your comments about the tongue's areas of sensitivity. Good luck.
-- Patrick A. Gainer (email@example.com), May 09, 2002.
Thanks for the comment. I prefer to take a medium mouthful of wine if color and nose are good, and then circulate it through all the oral and some parts of velopharyngeal cavity for best judgement. By the way, vitamin C is also good for offsetting the damage done to your mineral absorption by tannins in red wine (or coffee or tea, decaf or otherwise) when served before digesting and absorbing meals. Ferrous ascorbate complex seems better absorbed by body than free iron forms, even when impeded by tannic acid. Without vitamin C developers this posting would be of no relevance to photography!
-- Ryuji Suzuki (firstname.lastname@example.org), May 10, 2002.
Here's what I was doing wrong - as Patrick pointed out in a separate e-mail, very little water should be used when mixing the ascorbic acid with the baking soda. I tried this again last night using 20ml of water to mix 1/2 tsp of ascorbic acid and 1/4 tsp of baking soda. This mix fizzed for about 5 minutes before it stabilized and was then mixed to a total volume of 500ml of water with 5ml of Agfa Rodinal and used to process a roll of 120 TMX for 12 minutes. Agitation was an intial 30 seconds followed by 10 seconds every minute.
The results with the 1:100 Rodinal and ascorbic acid mix are wonderful. Compared to the straight 1:100 Rodinal and PMK negs of the same scene, the ascorbic acid/Rodinal print was not only dead on the money for contrast (at about EI 64) on Agfa MCP paper (~Grade 2 via no filtration), but the negative printed with considerably finer grain and slightly higher sharpness than the straight 1:100 Rodinal negative, was sharper and finer grained than the PMK negative, and had very very nice gradation of tones with bright highlights and rich shadow detail.
-- David R. Williams (email@example.com), May 10, 2002.