Archived posting to the Leica Users Group, 2007/07/25
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Since there is a bit of interest in chemical developers after the LuG being almost completely digital, I thought I'd post this. I wrote it for a newsletter a few of us here in Adelaide write and send around to each other. A lot of this is based on discussions I've had with LuGer John Black. The formula for JB9 is entirely his - and it's elegent and effective. My own experiments in pH were initiated after discussions with him and follow an approach I developed from our discussions. What follows is a long rant about Kodak Xtol. Xtol is probably the best commercially available developer for 35mm film. Why is it so good? It is an ascorbate developer. Ascorbates are effective developers of silver– with about the same efficacy at developing as hydroquinone, but the development by-products of ascorbates are acidic and act as development inhibitors. These by-products inhibit development proportionally to exposure (i.e. they inhibit more in dense areas of the negative and less in thinner areas). All ascorbate developers are, therefore, compensating developers with high acutance, dependant to some extent on the other components of the developer. This is good for tonality. ‘Compensation’ is claimed for many developers, but the ascorbate ones are among only a few where it has any real scientific basis or measureable effect. Kodak’s chemists were clever with Xtol in several ways beyond using an ascorbate as the primary developing agent. They added enough sulfite that the stock solution can be used as a grain-reducing developer and as a replenishment developer where the only replenisher needed is more Xtol. This sulfite concentration, combined with high activity, allows the developer to be used at dilutions of up to 1+1, 1+3 or 1+5 depending on the film being developed. This results in enhanced edge effects; it maximises direct development and minimises solution or physical development (called ‘solvent action’), increasing sharpness. They also used dimezone-S as the superadditive co-developer. Dimezone-S is a potent developer at low concentrations (it is, after all, similar to phenidone) but is easier to dissolve in water than phenidone and is less likely to oxidise once in solution. Properly mixed Xtol is actually quite stable – not Rodinal or PMK Pyro stock stable, but very good. So it’s sharp and has great tonality. Super. Unfortunately, Xtol got a reputation early on for both failing catastrophically and leaving odd artefacts in negatives. So, what gives? Is it great or does it suck? As usual, the answer to both is yes. Xtol fails for two reasons. Ascorbates are strong antioxidants and will scavenge oxygen from solution. Unfortunately the oxidation products of ascorbates do not develop latent silver images and do not present a colour change in solution. This explains what we already know – Xtol can die without warning. The other reason Xtol can fail is that the oxidation of ascorbates is catalysed by metal ions in water – particularly divalent cations (they are the 2+ ones). These include calcium and iron, the former common in ‘photo grade’ chemicals and the latter common in tapwater. Odd donut-shaped dots on negatives developed in Xtol are seen sometimes even by people who are careful about air and mixing. I suspect this occurs when impure dilution water is used and a little particle of iron or some other substance ends up onthe film, oxidising the ascorbate (and therefore inhibiting development) forsome distance around. It’s not likely tobe in the original mix water, since impurities here would probably kill the developer, unless it was mixed and then used almost right away. “Sudden Xtol death syndrome” can be fixed by keeping bottles completely full and in the dark; “Xtol spots” can be avoided by always using distilled or deionised and filtered water to mix and dilute Xtol. Whether you think that is worth the bother is up to you. I think it is. Can you mix your own Xtol? Sort-of. Mark Rabiner sent aroundthe basic formula from the patent (that’s not an MSDS – an MSDS is the “material safety data sheet” and the one for Xtol can be accessed by going here: http://www.kodak.com/eknec/PageQuerier.jhtml?pq-path=2879/4648&CID=go&idhbx=msds&pq-locale=en_US&_requestid=2627 and typing Xtol in the product name box) which comes from the patent. There are, however, indications from the physical behaviour of Xtol that what Kodak sells is somewhat different. Xtol stock solutions have a pH of 8.2 (what Kodak says); diluted to 1+3 the pH rises to 8.3-8.4. If you make the patent version, the startings olution is 8.35-8.4 and it stays fairly stable with dilution. Those pH differences might not seem like alot, but they’re important. The version from the patent is also about 30% less active. What does this tell us? The‘weakly alkaline’ (Kodak’s terminology) pH must come from a buffer, rather than just from metaborate and metabisulfite. I suspect a small amount of boric acid (i.e. a metaborate-boric acidbuffer) – it makes the most sense chemically; I also have some supporting data frommass spectroscopy analysis of commercial Xtol. The EDTA is also probably not enough on its own to sequester the divalent cation concentrations that Xtol can handle – I did this by adding known concentrations of dilute cation solutions to Xtol and self-made analogues and comparing them. So, what can you really do? Buy Xtol, of course. But if you really want to make a substitute, the following are options: Patrick Gainer’s PC-TEA 9 grams ascorbic acid .25 grams phenidone 100ml triethanolamine (TEA) Heat the TEA in a pyrex container in themicrowave for 30 sec.-1 minute, and add the ascorbic acid. When it isdissolved, add the phenidone. Be careful, because the TEA will get VERY hot. Dilute the concentrate 1:50 for use. PC-TEA is very good and if you have access to cheap TEA as those in the US do through www.chemistrystore.com it costs hardly anything. It’s grainier than Xtol, however, and doesn’t change its characteristics when diluted more. It works because it is very alkaline, which I think contributes to the grain characteristics of films developed in it. Many other ascorbate formulae have these flaws – the absence of the weakly alkaline pH, low sulfite concentration (but withsome sulfite still present) and the increase in activity with dilution are what make Xtol extraordinary. John Black’s JB9 is functionally the same as Xtol, but you mix it yourself. The developer is made from 3 liquid concentrates that are stable for at least 6 months, perhaps a year (stability testing underway). Store the solutions in glass bottles, tightly capped. The solution A should be store in the dark (a closed cabinet is fine) or in an amber bottle. Solution A: (Phenidone, ascorbic acid) Phenidone 1.25 gm Ascorbicacid- 50.00 gm Ethyelene or propylene glycol or dry methanol- 600 ml Warm up solvent to hot tap water temp before dissolvingcomponents. They will dissolve at about 100-125F. Dissolve ascorbic acid first. Solution B: TBE (Tris-borate-EDTA) Sigma cat# T3913 One 1L dry pkg dissolved in 1L DI water Other buffer concentrates may be substituted if made up to about half molar at a pH of about 8.3. Boric acid-metaborate(BA/Kodalk) would be fine, you may have to fiddle a bit to get the right pH. Solution C: Saturated Na Sulfite solution Na Sulfite(anhydrous)- 180 gm Distilled water- 600 ml Stir vigorously for about 30 min. Temp will rise a bit and it will almost all go into solution. Let stand overnight to equilibrate (some will crystallize out). Use after that. JB9 developer: SolA: 10 ml SolB: 50 ml Sol C: 20 ml Distilled H2O Fill to 250 ml Add sol B and C to water first, mix and then A (protects phenidonefrom oxygen in water). This is enough todevelop 1 roll of 35mm film. Scale up as necessary. Works best as a 1 shot developer at 68F, with moderate agitation. I use 13 min for Tri-X. I’ve used the tris and metaborate/boric acid versions of JB9 and they are functionally identical to Xtol. You can modify the sulfite concentration as you like. One of the best things about JB9 from my perspective is that you can mix the developing agents to the same concentration as Xtol stock, but keep the same sulfite as Xtol 1+3 (or any other favoured dilution). This is great for films like TMX and Acros that run out of developer in Xtol 1+3, or for pushing TMZ. Of course the other option is to mix the patent formula Xtol and addboric acid until the pH of the stock is 8.2, but you may also run into problems with 'photo grade' chemicals. I really don't think the EDTA alone is enough to chelate ions out of the chemicals or water. Also look at US patents # s 3658527, 5376510, 5503965, 5738979, 6110655, 6489090, 6673528 and 6686135 in addition to the Xtol patent 5756271. I hope this explains a few things and is interesting. Marty -- We've Got Your Name at http://www.mail.com! Get a FREE E-mail Account Today - Choose From 100+ Domains