C-41 negative mask consistency
I was wondering how consistent the density and colour balance of the orange mask used in colour neg films is?
Years ago I standardised on the now obsolete Fuji Reala for colour neg film for medium format.
My enlarger (Durst Modular 70 + Colour Micro head) has separate calibration channels for different types of film.
The assumption being that the filtration offsets required for a particular type of film do not change significantly
Calibration involves making test prints from a neg of a kodak grey card, measuring the print density and adjusting filtration until
you get a good colour match between the print and the original grey card.
In my experience, the mask used on Reala has been reasonably consistent.
However, I have had at least 2 batches where the mask is very different and requires considerable changes in filtration.
In particular, the last three films I've had processed appear very different to negs from a few years ago.
The difference is quite marked - even when comparing visually.
It can make adjusting filtration frustratingly difficult if you don't happen to have a grey card image on the particular film batch you are trying to make prints from.
What varies? The whole dye package or only the mask?
The mask density itself can be established by metering the unexposed parts of the film.
The orange mask appears different.
Originally Posted by AgX
If I measure the mask density using a Macbeth densitometer, I get...
Old batch of Reala negs:
R = 0.50
G = 0.81
B = 0.95
More recent batch of Reala:
R = 0.46
G = 0.95
B = 1.06
The density changes are different for each colour channel, so it affects the colour balance.
Unfortunately, I don't have an image of a grey card on the more recent batch of Reala, so I am unable to make comparative measurements.
I'm having to adjust the filtration by eye using an image that should be fairly neutral overall: A landscape shot on an overcast day.
If I make a test print of this image shot on the new batch of Reala using the calibrated filtration values from grey card on an old batch, I get an obvious blue/cyan cast.
If I use the enlarger scrambler and colour analyser to adjust the filters to give what should be an overall neutral, I still get a blue/cyan cast - albeit not as bad.
I have to reduce the Y & M filter values considerably to remove the cast.
That's when I started to wonder about differences in the orange mask.
The mask changing, and not the dyes, is something I don't believe can happen. If the mask changed and not the dyes you would not have proper color correction, the purpose of the mask. It is likely that the mask and the dyes are different, you just don't realize it. My guess is Fuji changed the emulsion for some reason, if it is only happening between older and newer batches. Has your processing changed at all? That could also change the color.
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You can visually check for this without a densitometer. Just develop a blank, unexposed section of film. That will give you an all-mask image,
and should serve as a reference provided all your developing variables have been properly monitored and kept constant. Different types of film can be significantly different in this respect, or even the same film on different bases due to different formats (sheet versus roll film, for example). I wouldn't implicitly trust any kind of generic preprogrammed factor about what the orange mask and fbf is "supposed to be". You have to fine tune every specific batch. But ya gotta do it for the paper batch anyway ... and it's pretty damn simple to balance test strips.
The numbers you show don't really seem to be that far off. Ordinary differences between emulsion batches and slight processing differences could account for what you are experiencing. As long as you can color balance your prints with no detectible image faults, I wouldn't worry about it.