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Old 22nd March 2009, 06:25 PM
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Default Does heat drying film cause fog?

Just curious because I recently started using my film dryer again, to avoid dust problems, and since then I seem to get quite high fog on everything I develop. I read somewhere recently that only slide film should be heat dried in colour photography (improves it apparently) so that's made me curious as to whether and/or how heat drying could cause fog.
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Old 22nd March 2009, 06:33 PM
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Can't see why it should but someone like Les should know for sure.
You are sure it's properly fixed?
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Old 22nd March 2009, 06:37 PM
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Never noticed that Rob. Is it possible that one of the chemicals you are using has deteriorated and is causing chemical fogging?
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Old 22nd March 2009, 06:44 PM
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Are we talking B&W film here? When I first started it was via a B&W night school class and without knowing any better we all stuck our films into the heated drying cabinet. I think it was set too high heatwise in order to get the throughput. There were often 20 students all developing films on the same night and the session only lasted 2.5 hours.

The only thing I ever noticed was that if you left the film in too long it would curl badly but I never noticed any effect on fog. It would eventually uncurl once cut up and placed in neg sleeves and put under a weight like a heavy book

Since then I have set up my own darkroom and have a drying cabinet but I just use the fan assisted ambient air setting. The film is bone dry in about 15-20 mins and no curl.

Comparing the heat dried films from my nightschool days to my ambient air dried films nowadays I can't see any difference.

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Old 22nd March 2009, 06:51 PM
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Ok this may have been a false steer cos I asked the question just after putting a film in to dry and this time I just used the fan without any heat. Same amount of fog which is 0.31 which I think is quite high. Maybe its just Delta films which do this. Delta 3200 was the same amount of fog with Microphen.
I used to get about 0.12 with HP5.
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Old 23rd March 2009, 01:24 PM
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Logically speaking there are no halides left in the emulsion so it's difficult to see what could fog. Perhaps there is some micro-reticulation of the gelatine or a physical change in the substrate caused by the heat? IDK. I guess you'd need to do an A/B test with the same two films processed together and one air dried and the other heat dried - one film cut in half after processing.
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Old 26th March 2009, 03:34 PM
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Quote:
Originally Posted by Andrew Bartram View Post
Can't see why it should but someone like Les should know for sure.
You are sure it's properly fixed?
That may be the problem. I have just been told that some delta films may need 7 or 8 minutes to fix fully. I normally do 5 mins in hypam 1+4. Will try longer fix time and report back.
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Old 28th March 2009, 04:11 PM
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I don't normally use delta, prefering hp5, but I have an odd roll of delta 400 and ilford recommemds 2-5 minutes at 1-4 for hypam/rapid fixer, which is the same as for hp5, and on the occasions I have used delta 400 I have fixed for 3 minutes in fresh fixer,so as long as your fixer is fairly fresh I don't think fixing is your problem,Richard.
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Old 28th March 2009, 04:31 PM
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As a follow up, I fixed a film for 8 minutes in Hypam 1+4 and it made no difference. I can only conclude that Ilfords Delta films have a higher base fog level than their non T-Grain films. I get similar fog with D400 and D3200 in various developers including HC110, Microphen, Perceptol and DD-X so its not specific to one developer.
It would be interesting to hear how much base fog others get. It's always around 0.3 + or - .02 so its pretty consistent. Not high enough to overly worry about but non t-grain films I have used often only give around 0.13 of fog.
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