Will the real Mytol please stand up

[albada]

The easiest thing to do is simply avoid ascorbates when scratch-mixing developers so that exotic sequestering agents aren’t needed.

Another way to avoid DTPA is to add the ascorbate (or ascorbic acid) just before using. But doing so constrains you to one-shot processing and thus no replenishment.

Mark

 

[Alain Deloc]

Another way to avoid DTPA

I don't want to avoid DTPA-Na5 because I have it as 40% solution. I just mixed a bottle of Xtol and tomorrow I will make first test.
I was thinking.. what if I would double DTPA quantity? Ron Mowrey's C41 formula asks for 8.43 g of this solution which translates into 3.37 g of dry product (3.3 times more than Xtol) and CD4 is far less temperamental than ascorbate being also protected by the HAS

 

[albada]

I don't want to avoid DTPA-Na5 because I have it as 40% solution. I just mixed a bottle of Xtol and tomorrow I will make first test.
I was thinking.. what if I would double DTPA quantity? Ron Mowrey's C41 formula asks for 8.43 g of this solution which translates into 3.37 g of dry product (3.3 times more than Xtol) and CD4 is far less temperamental than ascorbate being also protected by the HAS

First, I re-read your spreadsheet and now understand how you computed the weight of NaOH.

Regarding DTPA: The patent might have too little. Here are two comparisons from my notes:

(1) The MSDS for DDX states that 1-5% of the concentrate is DTPA-5Na. Based on its specific gravity, that is at least 13 g. It's diluted 1+4, which is 2.6 g/L in working solution. At least, and probably higher.​

(2) Fuji Patent 6878510 specifies 2 g/L of DTPA-5Na, twice Kodak's XTOL patent.​

These two data suggest that your 3.37 g/L is closer to what Kodak ships than 1 g/L.
If I were cloning Xtol as you are, I'd boost DTPA-5Na to Mowrey's 3.37 g and raise the pH to 8.2 by adding NaOH or s. carbonate.

Mark

 

[Milpool]

First, I re-read your spreadsheet and now understand how you computed the weight of NaOH.

Regarding DTPA: The patent might have too little. Here are two comparisons from my notes:

(1) The MSDS for DDX states that 1-5% of the concentrate is DTPA-5Na. Based on its specific gravity, that is at least 13 g. It's diluted 1+4, which is 2.6 g/L in working solution. At least, and probably higher.​

(2) Fuji Patent 6878510 specifies 2 g/L of DTPA-5Na, twice Kodak's XTOL patent.​

These two data suggest that your 3.37 g/L is closer to what Kodak ships than 1 g/L.
If I were cloning Xtol as you are, I'd boost DTPA-5Na to Mowrey's 3.37 g and raise the pH to 8.2 by adding NaOH or s. carbonate.

Mark

There are variables involved (pH of solution etc.) in how much is required. However note in the XTOL patent it is suggested the chelating agent(s) can be present in amounts up to 0.02 mol/l.

Note commercially available DTPA Na5 solutions (typically 40% in water) are alkaline, not acidic.

 

[albada]

Incidentally a decade or more ago (I can’t remember exactly when but I did discuss it with Dick Dickerson at the time) the metaborate was substituted with borax in commercially packaged XTOL.

This tells me that you have extensive knowledge of developers.
Can you recommend a quantity of DTPA-5Na?
Also, would boosting pH by adding s. carbonate increase buffering? I don't think so, but my knowledge of chemistry is poor, so I have no confidence in my analysis. @Alain Deloc wishes to clone XTOL, and that would mean not altering its buffering.

 

[Craig]

BTW, the XTOL patent specifies 1 g of DTPA*5Na for its "Dry Formulation", so that weight is for the dry powder and not a solution.
For your reference, here is a screenshot of the formula in the patent:

Speaking with my Patent Engineer hat on, don't take any example like this given in a patent as gospel. It's just what it says it is: an example of a B&W film developer. Which may or may not be Xtol. More likely than not, it only bears a passing resemblance to the actual formula Kodak used.

There are a few reasons for this, patents are usually filed fairly early in the development process in order to establish a filing date. R&D continues long after the patent application is filed, and in many cases a better/different way to achieve the desired result is found, and the original filing can't be updated.

Another reason is that that patent descriptions can be intentionally inaccurate. The inventor needs to disclose enough to protect what he wants, but that could mean that some ingredients are instead kept as trade secrets and omitted from the patent. Sometimes there is a deliberate intention to mislead competitors.

Also, specific sections in the patent specification mean different things. The general description carries no legal weight, only what is in the claims can be used to sue an infringer. The description simply serves to help define words in the claims. So you will often find that what is in the description is considerably broader and can contain material not in the claims, and also material that is unpatentable. View those sections only as general information, which may or may not be relevant to the material in the claims.

That's kind of a long winded way of saying that what is in the patent description might have nothing at all to do with the formula for Xtol that Kodak sells. Or it might be the exact formula. It is impossible to tell from the patent document.

 

[koraks]

@Craig, I get what you're saying, but given that the XTOL-derivatives that align closely with the patented formula appear to work identically to 'real' XTOL as manufactured, what's the practical implication of your words? Nobody's attempting to replicate XTOL-as-manufactured. The idea is to replicate it from a functional perspective. It's well-established that the patent formula is useful in that context.

 

[Craig]

@Craig, I get what you're saying, but given that the XTOL-derivatives that align closely with the patented formula appear to work identically to 'real' XTOL as manufactured, what's the practical implication of your words?

It was more in the general sense of don't assume what you see in a patent specification is 100% accurate and think that if you follow the formula you will get exactly Xtol (or some other photochemical if that is what the patent is for). Keep a healthy dose of skepticism and treat those formulas as starting points, not the "true" formula.

In this case, it does appear to be very close to commercial Xtol. That won't always be the case, I think we as a community happened to get lucky here.

 

[koraks]

Yeah, gotcha. I see what you mean, and overall, I agree. Having said that, it also seems that C41 patent formulas are fairly close to the real deal, or at least usably so. So while your caution is certainly justified, there's still utility in studying patents for this purpose, it seems.

 

[Alain Deloc]

C41 patent formulas are fairly close to the real deal

I mixed Ron Mowrey's C41 formula and it's far superior to many C41 developers which are sold today under various names (I tried a few, to be honest), and I'd say that it's almost as good as Tetenal C41, which produced the most accurate colors over the time.

 

[albada]

Regarding DTPA-Na5:
The MSDS for the 5-liter packets of XTOL say that DTPA is 1-5% of the packet's weight. That works out to 0.5 to 2.5 g/L.

 

[Alain Deloc]

However note in the XTOL patent it is suggested the chelating agent(s) can be present in amounts up to 0.02 mol/l.

Let's see.. DTPA-Na5 is having this formula C14H18N3O10Na5 --> C14H18N3O10Na5 is 503.25 g/mol. Patent says at the top of page 4 that "The sequestering agents can be present in an amount of from 0 to about 0.02 mol/l". I am going to use the maximum value and see what we get
503.25 x 0.02 = 10.065
It seems that 10.06 grams of DTPA-Na5 is the maximum value recommended by Kodak. The published formula inside the patent says 1 gram of DTPA-Na5. As @albada said previously, using a higher value as for Ron Mowrey's C41 is most likely a better idea.

 

[Alain Deloc]

Regarding DTPA-Na5:
The MSDS for the 5-liter packets of XTOL say that DTPA is 1-5% of the packet's weight. That works out to 0.5 to 2.5 g/L.

That's lower than what the patent recommends as maximum value. Of course, maximum value recommended by patent doesn't have to be the value used in the commercial formula. The commercial formula might have just 2 g/L and that fits very well between 0 and 0.02 mol/L

 

[Milpool]

This tells me that you have extensive knowledge of developers.
Can you recommend a quantity of DTPA-5Na?
Also, would boosting pH by adding s. carbonate increase buffering? I don't think so, but my knowledge of chemistry is poor, so I have no confidence in my analysis. @Alain Deloc wishes to clone XTOL, and that would mean not altering its buffering.

I'm not sure I follow the buffering/pH question. I definitely would not move from the target pH of 8.2 so I would not use sodium carbonate. Metaborate in the original formula is what I would use unless I could figure out how to rebalance the formula to use borax (tetraborate) in place of metaborate and achieve the same target pH (probably adjustments to the two sulfites), which is what Kodak eventually did. At the time the change was made I was paranoid the working properties could have been altered so I reached out to Dick Dickerson. Some interesting discussion but he said there wasn't really anything special going on with metaborate per se in XTOL despite conjecture to the contrary regarding complexes/polyhydric alcohols etc. not important here). One additional non-photographic thing I thought could have potentially been impacted was the ease of mixing part A (containing the Dimezone-S) which is helped by the higher pH but I personally found no practical difference.

Regarding DTPA-Na5, I would suggest more than 1g and probably more than is in packaged XTOL. My reasoning here is that the iron and copper impurities you are trying to chelate aren't just a function of water quality but also the purity of the other compounds - particularly sulfite. My guess (for what it is worth) is that the formulation in the patent assumes commercially prepared/packaged dry ingredients which would typically be better than the "technical grade" bulk ingredients us tinkerers usually have easy access to. As for how much DTPA to use though, I really don't know. Splitting the difference in the patent and going with say 0.01mol/l gives roughly 4g/l DTPA or 5g/l DTPA-Na5 maybe?

 

[Alain Deloc]

target pH of 8.2

Kodak patent recommends a pH between 8.0 and 8.5, so any value in between is basically ok.
I mixed it yesterday with substitutions (metaborate to borax, metabisulfite to sulfite and sodium ascorbate to ascorbic acid) and the resulting pH was 8.3 (right in the middle of the recommended interval).
I made a test with a piece of Fomapan 100 and it went black after 5 minutes. After that I doubled the amount of DTPA-Na5 just to be sure (it was 1g, now there are 2 g) and pH raised to 8.4, so I decreased it with acetic acid down to 8.3.

4g/l DTPA or 5g/l DTPA-Na5 maybe?

Probably 3.5 g/l is most likely an good value, as it's also the value recommended by Ron Mowrey for his C41 developer formula.

 

[koraks]

Kodak patent recommends a pH between 8.0 and 8.5, so any value in between is basically ok.

Well, yes, as long as the final pH after adjustment is 8.2 - or you'd have to revise the development times for the pH you end up at.

I'm not sure I follow the buffering/pH question. I definitely would not move from the target pH of 8.2 so I would not use sodium carbonate.

I can see what @Alain Deloc might have been hinting at (Alain, correct me if I'm wrong). Adding carbonate will shift pH up, but if you then adjust with e.g. acetic acid, you end up with a buffer of a higher molarity. The buffering action is effectively stronger/more robust. But pH adjustment is needed to set the buffer at the desired pH.

 

[Alain Deloc]

Adding carbonate will shift pH up

From what I have seen, increasing DTPA-Na5 weight above the 1 g from the formula will increase the pH anyway and has to be decreased with acid. I have no idea if more buffering is needed in order to add sodium carbonate over the rest of the chemicals.

 

[Milpool]

Well, yes, as long as the final pH after adjustment is 8.2 - or you'd have to revise the development times for the pH you end up at.



I can see what @Alain Deloc might have been hinting at (Alain, correct me if I'm wrong). Adding carbonate will shift pH up, but if you then adjust with e.g. acetic acid, you end up with a buffer of a higher molarity. The buffering action is effectively stronger/more robust. But pH adjustment is needed to set the buffer at the desired pH.

Understood. I guess I don't see the point of straying from the "original" though when it comes to buffering strength. If anything I'd want as close as possible to the buffering strength of XTOL (at target pH) and not more (or less of course).

In reference to Alain's earlier comment about the pH range in the patent, in this case we know XTOL is 8.2 and that is what I would target.

 

[albada]

I must laugh at the XTOL patent. In the "summary of the invention" near the beginning, it says "borate as the sole buffer", yet the formula includes both sulfite and metabisulfite, which form a second buffer (the first is s. metaborate or borax). As @Craig posted, patents can contain shenanigans.

 

[Craig]

I must laugh at the XTOL patent. In the "summary of the invention" near the beginning, it says "borate as the sole buffer", yet the formula includes both sulfite and metabisulfite, which form a second buffer (the first is s. metaborate or borax). As @Craig posted, patents can contain shenanigans.

In patent language, the "Summary of the invention" is just the claims paraphrased. So perhaps they had to claim only one buffer, as two might have been unpatentable.

 

[Rudeofus]

In patent language, the "Summary of the invention" is just the claims paraphrased. So perhaps they had to claim only one buffer, as two might have been unpatentable.

The sections before the claims section are more than just random drivel. A patent has to be written in a way, such that "a person skilled in the field can reproduce the results". This means: whatever is described in the "Summary of the invention" and the "Detailed description" sections will yield something, which does whatever it says it does. Mixing the formulas from these two sections will give you a working B&W developer, but of course not necessarily the exact XTol.

If people here already claimed "XTol isn't much different from D-76", then subtle differences between whatever is described in the patent and the real XTol will likely matter even less.

Kodak patent recommends a pH between 8.0 and 8.5, so any value in between is basically ok.

Kodak covered a whole pH range, such that someone in the same market can not raise pH by 0.1 and proclaim "that's not the dev from the patent!". There's reason to assume, that moving outside this specified pH range will likely yield an at least very different developer.