Troubleshooting spots on film - lab or back issue?

[brdo]

I've been having some problems with these lines of spots on 120 roll film.

I'm unsure if it's a lab issue (drying spots?) or an issue with one of my film backs, but I've inspected them closely and can't find anything that could be the culprit. It'll only be on 1 of every 5 or 10 rolls, and the size and location of the line seems to be different shoot to shoot.

The attached image is a crop from a 6x7 frame, the lines are always in the same direction down the length of the roll, which would be the direction debris in the back would damage then film but also the direction film would be squeegeed.

Any ideas?

 

[loccdor]

It does look like a lab issue to me. If it was camera related you would expect it to be in the same place all the time which you stated it is not.

Perhaps some mineral build-up on their rollers. I would try switching labs or home development - or if you find your lab particularly responsive you can try talking to them about it and they might fix the problem as well as give you some kind of compensation.

You can usually tell a mineral/water hardness mark from a development problem by rotating the film in side-light. The development problem would look the same from all angles while the drying problem would become brighter or darker depending on the angle of the light and also be more visible on one side than the other.

 

[Tel]

It would help if you could post pictures of the entire width of the negative in addition to the cropped pictures above. First impressions: these look like marks made by liquid residue on the film; marks made in-camera are made when the film is dry and tend to be scratches rather than blobs like these, hence the likelihood that these are the fault of your lab. The fact that it doesn't happen on every roll tends to reinforce that idea. I recall several rolls of mine that came back from the lab with "tractor marks" (impressions clearly made by a wheel with a tread pattern) indicating that the machine that did the processing had some sort of rubber wheel that touched the film at some point and left its imprint. My solution was to start processing C-41 in my kitchen, and I've never gone back.

 

[koraks]

these look like marks made by liquid residue on the film

Yeah, they look like that to me, too. Reminds me of machine processing C41 with a stabilizer as the final bath and an exit roller that leaves a trail of droplets that dry up and leave residue.

 

[Sanug]

Are the spots visible on the film base or on the emulsion? Have you tried to wash and wipe the film? Maybe the residue will go away.

 

[NortheastPhotographic]

Stabilizer. Were to you re-wash the negative they'd go away. Or just to the fast way and quickly retouch the scan in PS.