Random color shift while printing

[Matt Brown]

Hey Everyone,

So I had a strange, seemingly random experience in my color darkroom yesterday. After making a few perfectly-balanced 8x10in prints, I suddenly got a completely cyan print. Thinking it was an anomaly, I put another sheet of paper through and got a second cyan print. The chemistry was fresh and reliable and so was my paper, so before dumping chemistry and starting over I simply decreased my Y&M filtration by 20. At that point, I had a color-balanced print again.

This isn't really a problem; I've printed a lot in the past few days and this hasn't happened again. I'm just wondering what would cause a sudden, erratic filtration change.

My specs are pretty simple - I shoot Fuji films (Pro 160S and Pro 400H), develop prints in Fuji RA-4 chemistry, and print on Crystal Archive Type II. My enlarger is a Durst M670.

Any thoughts would be interesting to me!

 

[frotog]

Hi, Matt Brown,

What you describe sounds like color temperature drift due to the age of the projector bulb in your enlarger. As the tungsten filament ages, color temperature goes down, most often accompanied by a asymmetric spike in the red part of the spectrum hence the sudden appearance of cyan in your print. Try a fresh enlarger lamp and you should be good to go (albeit with a different filtration pack).

 

[hrst]

Variation in mains voltage is a more probable explanation for a sudden color temperature drift.

I have never noted any differences in color temperature between old and new bulbs. When I last changed a bulb that was used for years and was burned out, there was no change in filtration (I used the same type of bulb, naturally.)

Did you notice a change in exposure needed? If the culprit was the bulb, then you would have needed to increase the exposure quite a bit (probably doubled or so) in addition to changing the filtration.

 

[greenrhino]

Another possibility is that it was a pure mechanical error. I have had the filtration arms that hold the dichroic filtration on d5's get stuck and then move suddenly and cause exactly that kind of anomaly

 

[hrst]

Yes I agree, it's probably the most probable explanation.

 

[Matt Brown]

Thanks, everyone, for the responses.

Having done a little detective work in the building, I believe the culprit is a variation in voltage...possibly combined with the age of the bulb. Right below my darkroom is a working biofuel plant, and they've recently installed some kind of equipment that is causing power fluctuations all over our building.

And hrst, I did have a change in exposure, but it was actually in the opposite direction. I start all of my prints at f8 + 15 seconds, but after the sudden cyan shift, I had to stop down to f11 to get a print. Probably should have mentioned that before!

 

[Matt Brown]

Another possibility is that it was a pure mechanical error. I have had the filtration arms that hold the dichroic filtration on d5's get stuck and then move suddenly and cause exactly that kind of anomaly

Hey greenrhino,

I thought this could have been a culprit, too, so I removed the diffusion box on the enlarger. I played with the filtration for a minute or two and nothing seemed to be out of the ordinary.

 

[hrst]

And hrst, I did have a change in exposure, but it was actually in the opposite direction. I start all of my prints at f8 + 15 seconds, but after the sudden cyan shift, I had to stop down to f11 to get a print. Probably should have mentioned that before!

Sounds really weird. Higher voltage -> more light output -> shift towards blue due to increased temperature of the filament. That is, all wavelengths are increased, but blue more than green more than red, so that when the exposure is compensated, there is less red than before. Less red means more red print.

OTOH, lower voltage -> lower light output -> shift towards red. Then you would have cyan prints, but definitely would need to increase exposure.

Or am I mixing something up?

So the print was cyan also after stopping down the exposure, and you ended up decreasing Y&M (= R). This would have been perfectly understandable if you had to INCREASE your exposure... (OTOH, decreasing filtration increases exposure, so you could have been ended up with almost unchanged exposure. Anyhow, I can't understand how it goes in the opposite way!)