Quick question about making D-23.

[Yezishu]

Doesn't heat degrade Ascorbic Acid as well at a temperature as high as 200 F? According to scientific literature it does and IIRC @albada worked at a much lower temperature for his long lasting Mocon concentrate.

For the Ascorbic Acid dry solid, it decomposes at 191 °C (https://doi.org/10.1016/j.jpba.2013.01.018). I don't know the decomposition temperature in TEA (might be much lower, as in water), it seems that Gainer initially reported that using 110 to 120 °C (250 F!) is also safe. But I prefer mixing at lower temperatures, as mentioned earlier, I don't like thick, hot liquids that don't emit steam, it's very likely for me to misunderstand that they are not so hot.

 

[koraks]

I'd strongly recommend to keep mixing temperatures limited to 50-60C. With stuff like TEA and glycol, the safety risks of working above the boiling point of water just aren't worth it. The burns you can get that way are really nasty; ask me how I know. Quite painful.

 

[Raghu Kuvempunagar]

For the Ascorbic Acid dry solid, it decomposes at 191 °C (https://doi.org/10.1016/j.jpba.2013.01.018). I don't know the decomposition temperature in TEA (might be much lower, as in water), it seems that Gainer initially reported that using 110 to 120 °C (250 F!) is also safe. But I prefer mixing at lower temperatures, as mentioned earlier, I don't like thick, hot liquids that don't emit steam, it's very likely for me to misunderstand that they are not so hot.

Decomposition no doubt requires higher temperature, but Ascorbic Acid starts degrading at modestly high temperatures. There are works that report substantial degradation of Ascorbic Acid in food when cooked at temperature of 80 C. Now, Gainer might have used sufficiently more Ascorbic Acid in his formulation that off-set the loss due to heat degradation. But I am not aware of any tests that he did to compare the activity of PC-TEA developer made from his concentrate with that made by dissolving the ingredients directly in water at the prescribed dilutions. I remain skeptical of any developer concentrate involving Ascorbic Acid and high temperature.

 

[dcy]

Your experience is valuable, while methods can vary based on the situation. I have an heated magnetic auto-stirrer, so there's no need for high temperatures to speed up dissolution. I simply add everything to TEA and stir at 60-70°C overnight or for a few hours. (Not a suggestion, just a casual chat.)

There are various approaches to achieve the same target if we understand what the goal is, such as using a microwave to heat up TEA to 120°C(manual stirring) or a boiling water bathauto/hot plate to reach 80-90°C(more manual stirring). Each method has its pros and cons. Personally, I prefer avoiding the risk of spilling hot liquid out, though many have the skills to handle it safely and hope to complete the mixing quickly, either way is fine..

Yeah. I also use a heated magnetic auto-stirrer. I was surprised at how much ascorbic acid you need to add, and how much it just doesn't want to dissolve. It was like an iceberg of ascorbic acid floating on the TEA. I kept increasing the temperature. I think I hit 90°C before it all dissolved. That thing looked like it could cause a serious burn. I'm glad I didn't have to stir 120°C TEA by hand.

 

[dcy]

Doesn't heat degrade Ascorbic Acid as well at a temperature as high as 200 F?

No idea. Thankfully I didn't quite hit that temperature, but I got real close. My notes say to aim for 90°C (194°F) next time; so I must have reached 90°C or just below that.

 

[dcy]

There are works that report substantial degradation of Ascorbic Acid in food when cooked at temperature of 80 C.

I think I heated my TEA above 80°C.

 

[Yezishu]

Decomposition no doubt requires higher temperature, but Ascorbic Acid starts degrading at modestly high temperatures. There are works that report substantial degradation of Ascorbic Acid in food when cooked at temperature of 80 C. Now, Gainer might have used sufficiently more Ascorbic Acid in his formulation that off-set the loss due to heat degradation. But I am not aware of any tests that he did to compare the activity of PC-TEA developer made from his concentrate with that made by dissolving the ingredients directly in water at the prescribed dilutions. I remain skeptical of any developer concentrate involving Ascorbic Acid and high temperature.

You're right, but as the purpose of TEA here is to avoid water and to lock metal ions to prevent degradation, the lifespan of Vitamin C in TEA might be significantly longer than in aqueous solutions(food) even under higher temperature.
Gainer conducted experiments on Vitamin C aqueous solution developers before PCTEA (such as, https://web.archive.org/web/20011024073823/http://unblinkingeye.com/Articles/VitC/vitc.html), using ~2g/L concentration, which is consistent with what he published as PCTEA. I believe he would mention significant degradation if he found it.

 

[Raghu Kuvempunagar]

Gainer conducted experiments on Vitamin C aqueous solution developers before PCTEA (such as, https://web.archive.org/web/20011024073823/http://unblinkingeye.com/Articles/VitC/vitc.html), using ~2g/L concentration

You're right. 1 l working solution of PC-TEA at dilution 1:50 contains developing agents in the same ballpark as Gainer's Vitamin C developers. However, the former is supposedly equivalent in strength to D-76 1+1 whereas the latter is equivalent to D-76 stock. So their activity is not quite the same despite similar amounts of developing agents. This could partly be due to the use of TEA in PC-TEA and partly due to loss of potency resulting from high temperature mixing. Without a proper test that compares PC-TEA working solution made from the concentrate with that made by dissolving the ingredients of PC-TEA directly in water at 1:50 dilution, we can't be sure.

 

[Donald Qualls]

If I have interpreted what you have said correctly and I happen to be someone who craves certainty then it sounds better not to add a pinch of sulfite

The color change indicates oxidation (oxidation products of p-aminophenol derivative developers are red to brown in color, that's why old Rodinal looks like Coca-Cola). Preventing it shows that the oxidation has been avoided. I don't know what's confusing about that.

 

[Yezishu]

You're right. 1 l working solution of PC-TEA at dilution 1:50 contains developing agents in the same ballpark as Gainer's Vitamin C developers. However, the former is supposedly equivalent in strength to D-76 1+1 whereas the latter is equivalent to D-76 stock. So their activity is not quite the same despite similar amounts of developing agents. This could partly be due to the use of TEA in PC-TEA and partly due to loss of potency resulting from high temperature mixing. Without a proper test that compares PC-TEA working solution made from the concentrate with that made by dissolving the ingredients of PC-TEA directly in water at 1:50 dilution, we can't be sure.

I agree that rigorous comparisons are needed to confirm the effects of heating ascorbic acid in TEA. The pH of PCTEA 1:50 is about 9, whereas Gainer‘s aqueous developer had a pH of 10.8. This might explain part of the activity, but might also not all of it.

Unfortunately, my PCTEA has never been dissolved at high temperatures and thus cannot serve as an example. When unopened they are almost colorless. Perhaps others here have more extensive experimental experience to share?

 

[Dave Lusby]

I used to use the "teaspoon" method for mixing D23. But after I was gifted an accurate scale, I started using it and found the results, in terms of developer action, to be much more consistent.

 

[Yezishu]

Yeah. I also use a heated magnetic auto-stirrer. I was surprised at how much ascorbic acid you need to add, and how much it just doesn't want to dissolve. It was like an iceberg of ascorbic acid floating on the TEA. I kept increasing the temperature. I think I hit 90°C before it all dissolved. That thing looked like it could cause a serious burn. I'm glad I didn't have to stir 120°C TEA by hand.

Let me guess what happened. My ascorbic acid forms large crystals that settle at the bottom, while yours might be a loose, airy powder that floats on the surface with a larger volume. It might be helpful to moisten the ascorbic acid powder with a bit of ethanol or isopropanol before adding TEA.

 

[pentaxuser]

The color change indicates oxidation (oxidation products of p-aminophenol derivative developers are red to brown in color, that's why old Rodinal looks like Coca-Cola). Preventing it shows that the oxidation has been avoided. I don't know what's confusing about that.

Thanks Donald So, just so I can be clear, you do support and use the " pinch of sulfite" first when mixing D23?

pentaxuser

 

[Donald Qualls]

Thanks Donald So, just so I can be clear, you do support and use the " pinch of sulfite" first when mixing D23?

pentaxuser

I do.

 

[dcy]

Let me guess what happened. My ascorbic acid forms large crystals that settle at the bottom, while yours might be a loose, airy powder that floats on the surface with a larger volume. It might be helpful to moisten the ascorbic acid powder with a bit of ethanol or isopropanol before adding TEA.

Yeah. I grabbed Vitamin C from the pharmacy and ground the pills down into a fine powder with a mortar + pestle. I realized too late that that was probably not the best idea --- pills meant for human consumption probably have a coating and/or a binding agent and who knows how that's going to affect my PC-TEA.

 

[Donald Qualls]

pills meant for human consumption probably have a coating and/or a binding agent and who knows how that's going to affect my PC-TEA.

The main thing is the starch and waxes used to bind the medicine into a solid pill. I use acetaminophen (from Costco, due to price) for my Parodinal, because it's difficult to buy the pure stuff -- and there's always some insoluble residue after crushing and dissolving the caplets, but the sodium hydroxide is strong enough to break those impurities down along with the active ingredient and they don't appear to have any photographic effect. FWIW, you can buy either ascorbic acid powder or sodium ascorbate (not the same for formulae due to pH difference, but both provide ascorbate in solution) from nutrition stores or on Amazon. In either case, the powder in the bottle is food/drug/supplement grade and better than 97% pure, no fillers or binders.

Given there's no very high pH component in PC-TEA, you're likely to find the insoluble material as particulates in the final developer -- which can leave clear spots on your negatives (which will read as black specks in the scan or print). If you don't see enough of those to cause trouble, I wouldn't worry about it for your current batch -- but it's worth getting the pure stuff for next time.

 

[pentaxuser]

I do.

Thanks, seems pretty well all parties agree on the importance of the pinch of sulfite with the apparent exception of Kodak, based on its quote in one of the posts?

On balance it sounds as if sticking to the pinch of sulfite prior to the addition of metol is worthwhile

pentaxuser

 

[Donald Qualls]

On balance it sounds as if sticking to the pinch of sulfite prior to the addition of metol is worthwhile

At the least, it's harmless.

 

[pentaxuser]

At the least, it's harmless.

Thanks I hope the above always describes me as well

pentaxuser