Boost film-speed with simple reversal process?
This sounds too good to be true. But the passage below is from Grant Haist's "Modern Photographic Processing", Vol II page 360-361. He is as reputable as they get. He describes a way to gain two stops of film-speed in B&W film by the following reversal monobath development:
In 1954 Hutson K. Howell used the reversal monobath to increase the film speed with most negative films. After being processed for the recommended time with continuous agitation, the film, saturated with developing solution, was exposed to a bright light (10 sec to a No. 1 Photoflood bulb at a distance of 1 ft), forming the positive image. An acid rinse or acid hardening bath completed the reversal processing. The composition of the monobath varied with each photographic material, but the following formula was successfully used with the higher-speed films:
Water .................................... 800 ml
Metol ..................................... 5 g
Sodium sulfite, desiccated ...... 50 g
Hydroquinone ......................... 20 g
Sodium hydroxide ................... 20 g
Sodium thiosulfate (anhy) ........ 54 g
Water to make ....................... 1 liter
Developing time was 3 to 5 min at 68F.
The original camera exposure is critical, and Hutson K. Howell recommended that four times the normal exposure index be used.
Note that there is no fixer bath. This technique makes me ask several questions: If this does such a good job of boosting speed, why aren't people using it these days? What is the image-quality like? Will it work with t-grain films? If anyone has any experience or comments about this speed-up-by-reversal-monobath idea, I'd like to hear them.
I can't answer your question Mark, but I will have to give this a crack tonight and see what I get.
Cheers - Andy C
16mm Cine, 35mm, 120, 5x4 & 7x5.
Mark, I did a lot of workm on monobaths in the late 1970s there's something missing in this process.
A good vbasic monobath is Crawley's FX-6a
Crawley FX-6A Monobath
Sodium Sulphite (anhyd) 50.0 grams
Hydroquinone 12.9 grams
Phenidone 1.0 gram
Sodium Hydroxide 10.0 grams
Sodium Thiosulphate 90.0 grams
Water to 1 litre
Develop for 15-20 mins Monobaths in practice develop to completion of the fixing component after which no development can take place.
It's nomal to tweak a monobath by varying the Thiosulphate level from 70gm per litre to 125 gm per litre to suit the film.
Not so different, the fact that one's MQ and the other PQ has no real impact, Howell's monobath is more concentrated though hence the shorter development time. (Crawley's monobath uses normal Thiosulphate not anhyd)
Now the problem is that Howell's monobath will produce a negative image in 5 minutes, there's no reversal bleach, so even if the fixing component hasn't been completed before the reversal exposure to the photoflodd any positive image will be weak and alongside the existing negative image. So there's something missing here.
Ian: Elsewhere (and sorry I didn't quote it), Haist explains the principle behind this. The thiosulfate is more active in areas of high development (ie, high exposure), and less active in areas of low exposure. So if the remaining silver halide is exposed after development, you get a positive image. The result is a weak negative image and a denser positive. Haist says that a process like this can produce high contrast images, with high minimum density due to the negative image. Note that some silver halide needs to remain, so the fixation in this monobath must be partial.
Originally Posted by Ian Grant
That makes sense but then emulsions in 1954 were quite different to those we use today, they were thicker coatings and had a higher silver content.
My experience would suggest that the 5 minutes development time might well be too long for modern emulsions and the negative image too strong for subsequent reversal.
In addition the 4x the film speed is based on the old ASA/BS speed ratings before they were revised upwards in the early 1960's so in reality the claimed increase is just 2x or 1 stop.
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I'm just starting to look into the idea of reversing B&W negative film (I want to project Adox CMS 20 and Neopan 1600) and reading through the instructions for reversing Tmax, it says you should expose at 50 instead of 100:
I've successfully used Crawley's MB to produce good quality negatives. Different films may need differing amounts of sodium thiosulfate in order to control excessive highlight density. I've used it with Lucky film, Efke 50, and good old Tri-X. I'm having trouble imagining how this will work, though. Maybe one day I'll give it a go.
The tone of that article makes it sound like supposition based on second-hand information.
In other words, the author never actually did the process but only read about it or spoke to somebody else who did. He's just reporting that information and adding his own commentary on top.
It's a lot like the way people who wrote opinions, back in the 1950's, and said things like, "In the year 2000, there will be a "flying car" in every garage."
There's no way to prove or disprove a prediction that can't come true for more than 50 years. Besides, who's going to be around to judge whether it is true? Still, people would read this kind of thing and take it as gospel.
I see a few red flags in the way that article that was written which tells me that the author is bullshitting his way through the subject.
I didn't say he always wrote bullshit. I'm just saying this particular article smells funny.
I have a long article in an old BJP Almanac on th e history etc of monobaths, one of the references is Grant Haist's 1966 "Monobath Manual". The important thing to remember is Haist is writing about someone elses claims, in this case probably published work by Hutson K. Howell rather than work HAist's done himself.
Having looked again at the formula and converted the Thiosulphate to the more usual Pentahydrated form which would be 84g/litre then it makes no sense as it's going to have stronger developing action than Crawleys FX-6a.
However it's likely this was a specialist monobath for a specialist application as Hutson K. Howell was manager of Itek's Photo Science and Photogrammetry. It's unlikely it was designed to give high quality reversal transparencies.
It's all supposing until given the old college try. I'm glad Andy C. is going to take a stab at it.
This certainly sounds like a bizarre process though.
I've been excited by a few processes that, when brought up to APUG, have been shot down for similar reasons; old films are different, it doesn't work, etc. Not saying that I don't believe these claims, but I guess we'll never really be convinced until we give them a shot for ourselves. For instance, I thought 'physical development' sounded like a panacea, but apparently it doesn't work(?).
Ok, but what I don't get is... if this is a monobath, the thio will be dissolving away the positive image while the negative one is developing. When the re-exposure comes, presumably the negative image will be done developing, and in turn the reciprocal silver-halide in those negatives areas will have been more thoroughly dissolved out (since "high dev = higher thio action") than say the silver-halide in wholly unexposed regions. But as the positive image develops, how can it ever exceed the density of the negative image? I guess the re-exposure is so intense that this is possible...
This sounds like photographic tight-rope walking!