Film Curling ( Cupping ) When Drying

Ian-Barber

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Ive just developed a roll of Tri-X 120 roll film and as I look at the film drying it's started to cup along the longe edge. Never seen this before with other films.

The film is weighted at the bottom with a piece of metal attached to a clothes peg to give it some tension.

Anyone else seen it happen and any advice if any to prevent it next time
 

David M

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#2
All roll film seems to enjoy curling. Rapid drying will make it curl more. The curl is normally longitudinal, the other way from to the way it curved on the roll. That is, it looks like a measuring tape. It's quite normal and a bit of a curse when scanning. Is it a very heavy weight? It only needs to be heavy enough to prevent rolling up, not to stretch the film.
 

Ian-Barber

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I think the issue was that I hung the film in the conservatory and it was very warm in there today, normally, I just leave it in the bathroom which is North facing and remains a lot cooler
 

Ian Grant

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#4
120 films have an anti-curl coating it varies between manufacturers, stick it in a neg sheet and it should flatten OK.

I dry films in Turkey much hotter than here and after a while there's no difference.

Ian
 

alexmuir

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#6
I found Tri-X quite sensitive to the drying conditions. I haven't used it for some time, but I think slower drying at a lower temperature produced a flat result. I once held a roll over an electric radiator to dry it in a hurry. It rolled lengthwise which was very difficult to deal with.
Alex.


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mpirie

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#7
If you want to see a film curl, try a roll of Rollei ATP.......you need at least 3 hands while trying to get it into the film holder for scanning!!

Mike
 

David M

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#8
A drying technique that I've never tried is to soak the film in meths or other alcohol, which dissolves the water, then set fire to it. Apparently, in skilled hands, this works well. Look for darkroom workers without eyebrows.

I presume that the normal, non-pyrotechnic method of drying induces more curling when the surface of the wet and swollen emulsion dries very rapidly and shrinks, pulling the film into a curve and creating a seal over the rest of the emulsion. The under-part of the emulsion then dries more slowly and sets like a party jelly, thus holding the curve. There must be optimum conditions of temperature, humidity and ventilation, even wetting agent. For all I know, the temperature of the final wash may be a factor. Does anyone know what they are, or which factor is most significant?
Or, as Mike suggests above, it might be an inherent characteristic of each film.
 

Ian Grant

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#9
I've used the alcohol drying technique, you use 2 or 3 baths of differing dilutions with water and the last 100% alcohol. You can dry a film in under 5 minutes, the 100% alcohol evaporates so quickly there's no need to set fire to it :D

The issue is getting 100% Ethanol which needs a licence for laboratory use, that's how I had access to it.

When I'm in Turkey ((except for the Winter) all B&W films get processed and washed at 27ºC, in the UK 20ºC, and I air dry naturally (no heat) I don't get any difference in curl. It does help to dry with a weighted clip on te bottom as they hang drying.

The worst films for curl were Foma, they've changed the base since I last bought some so I don't know what it's like now. Even with a bad curl I've never had an issue enlarging or scanning, the stay flat in the negative carrier or scanner holder.

Ian
 

David M

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#10
I rather suspect that someone was trying to impress a nicely brought up young lad with the fire technique. It was certainly faster than five minutes. Sadly, I don't remember its effect on curl. (Other than making my hair curl.)
Has anyone tried drying film on reels? I'm sure I've seen machines for this, but not recently. It should alter the direction of curl, but would that be better?
I don't remember finding curled film such a problem when using an enlarger – a nuisance, but not a problem. Getting curly film into a scanner's holder seems much more difficult and perhaps scanners are more sensitive to curl as they are not stopped down for increased DoF.
Presumably there are optimum conditions for minimum curl. They might be tucked away in a neglected PhD thesis somewhere. They might even have been published by a film manufacturer. Dunno.
 

mpirie

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#12
The alcohol technique has been around for a long time......probably from before the press photogs got hold of it.

We used to use the same technique with methylated spirit which was much easier to get hold of but left a residue. I never tried setting fire to it.......once the film had soaked for a minute all the water had been absorbed by the meths and it dried very quickly.......but archival properties were not a priority :)

There was a machine for drying film on the reels.....can't remember what it was called, but it'd be relatively simple to make your own......so long as you keep the air relatively cool (yes, reels will melt on radiators) :)

Mike
 

David M

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#14
I've just put down a tea towel.
A too-heavy weight on the film will induce more curl; it should be just heavy enough to keep the film hanging straight. If you take a piece of fabric (tea towel, handkerchief) and pull on it, you will see creases forming along the direction of the pull.
 

Alan9940

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#15
I put a wooden clothes pin on the end of roll film to provide some light tension. However, most every film I've ever used curled lengthwise or cupped; sometimes both. I put a sleeve of strips under various amounts of weight for days and weeks to no avail. I've come to the conclusion that it's simply a fact of life! ;)
 

Stephen Batey

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#16
Presumably there are optimum conditions for minimum curl. They might be tucked away in a neglected PhD thesis somewhere. They might even have been published by a film manufacturer. Dunno.
There's a few pages on drying in Grant Haist's Modern Photographic Processing, vol 1, p683-685 together with references to the literature. I haven't as yet read it - just skimmed it - but it is there. Curl is discussed...
 
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