How do you filter your C-41 chemistry?

Certain Exposures · 2025-12-17T12:55:17-0500

Maybe I should step back a bit further. Have you ever needed to filter your C-41 chemistry? If so how did you do it?

I think there could be some sort of fine particulate forming in mine. I can't think of why it would be there. Maybe the tape in 120 rolls leaves it there?

Maybe this explains the dots I see on some negatives. However, the dots appear in a similar spots on the negatives. I doubt the particulate is that petty.

thinkbrown · 2025-12-17T13:26:24-0500

Yeah, all replenished chemistry picks up crap over time. I use coffee filters when I'm pouring stuff back in the bottle after a session, seems to do the job for me

gbroadbridge · 2025-12-17T15:08:11-0500

Certain Exposures said:
Have you ever needed to filter your C-41 chemistry?

Maybe the tape in 120 rolls leaves it there?

I've never seen an issue, however I rinse between every stage so there is very little chemical carryover (which I suppose may cause some unwanted chemical byproducts)

Film should be clean going in, so should be clean coming out the other end with nothing detaching in the processing baths.

I remove the tape from 120 roll film when loading on the reel.

loccdor · 2025-12-17T15:31:18-0500

I use the liter kits for about 16 rolls and then toss them. I do more prewashes/intermediate washes between steps than is recommended so my risk of contamination should be reduced.

Other than silver particles collecting in the blix as the kit gets more thoroughly used, hasn't been a problem. I edit out any occasional bright flecks of silver in the image with clone brush. Some people pour their fixer through coffee filters.

koraks · 2025-12-17T17:12:16-0500

Certain Exposures said:
Have you ever needed to filter your C-41 chemistry?

Nope. I use the developer and fixed one shot most of the time. The bleach doesn't throw down a precipitate. So I've never looked into filtering it. I did at some point have a problem with tiny little spots which turned out to be unrelated to the actual chemistry, but at that point I did switch over to one shot fixer and I never went back (even though it had nothing to do with the problem I ran into, in hindsight). I was already using the developer one shot at that point; I occasionally reuse it once within a short period of time after first use and that's always problem-free.

mshchem · 2025-12-17T18:14:13-0500

I'm one shot with developer. I've never fiddled much with filtering photo chemistry. I use demineralized (RO) water for chemistry.

Certainly nothing wrong with filtering. I would use a fast paper filter, qualitative, like the old Whatman #2, I'm sure a coffee filter would be OK.

Mr Bill · 2025-12-17T20:25:46-0500

FWIW commercial machines, using replenishment, always have built-in circulation systems (pumps) with replaceable filters. Most common were cylindrical filters with a 20 or 30 micron rating; maybe 10 micron for pickier users. These pretty much collect most of the sludge.

Samu · 2025-12-17T22:08:17-0500

The OP does not state what kind of system are we talking about. Is he talking about reusing a liter kit in handheld tanks, or about a replenished, commercial-style system?

gbroadbridge · 2025-12-17T22:47:26-0500

Samu said:
The OP does not state what kind of system are we talking about. Is he talking about reusing a liter kit in handheld tanks, or about a replenished, commercial-style system?

He does when he states he leaves the tape on 120 rolls, and wonders if that may be leaving a residue in the chemistry.

Therefore, he is re-using chemistry and processing many rolls with a kit that allows such use. q.e.d.

I do the same, and process 16 rolls with1 litre of chemistry before discarding it.
No problems in the last 20 odd years I've been doing it and I've never found the need to filter the chemistry

Samu · 2025-12-17T23:35:16-0500

gbroadbridge said:
He does when he states he leaves the tape on 120 rolls, and wonders if that may be leaving a residue in the chemistry.

Therefore, he is re-using chemistry and processing many rolls with a kit that allows such use. q.e.d.

I do the same, and process 16 rolls with1 litre of chemistry before discarding it.
No problems in the last 20 odd years I've been doing it and I've never found the need to filter the chemistry

If this is the case, any residue in chemistry is a reason to mix a new batch. C-41 chemistry costs next to nothing compared to film prices, and trying to reuse beyond capacity is basically ruining a $15 film in order to save 50¢. No developer will produce 16 rolls of film per liter unreplenished, if good quality negatives are desired. The main reason for many of the companies catering to hobbyists are claiming unrealistically high capacities of their chemistry, are the low expectations of folks mainly scanning. You can make an acceptable digital scan from a negative which is quite much off the industry standards. But if you print in a darkroom, this is not the case. Bad negatives are hard to woek with, or in the worst case, good results are impossible to achieve. In replenished systems, such as minilabs, filtering the solutions is necessary.

Hie didn´t say he was using a one liter kit. It is possible to use professional chemistry also in tanks or in rotary systems. That said, replenishing is probably not a viable option in this case for C-41 process.

gbroadbridge · 2025-12-18T01:05:23-0500

Samu said:
But if you print in a darkroom, this is not the case.

I agree, but statistically almost no one prints colour in the darkroom anymore 0.00001% does not count.

Samu · 2025-12-18T01:13:46-0500

gbroadbridge said:
I agree, but statistically almost no one prints colour in the darkroom anymore 0.00001% does not count.

You are exaggerating. Even in Photrio, there are many who do. And I am not the only one. And it is not even very hard, although the "photo club" types said even in the 1980´s it were almost impossible. But yes, unfortunately the young generation is fine with digital files in social media. This is true with any kind of printing photos, irrespective of the technology used.

gbroadbridge · 2025-12-18T01:19:21-0500

Samu said:
You are exaggerating. Even in Photrio, there are many who do.

The entire cohort of Photrio probably comprises less than 0.00001% of the folks using CN film worldwide, so that's not much of an argument

Last time I was in a film lab a couple of weeks ago, the lab operator had not even heard of Photrio.

So no, I'm not exaggerating

mshchem · 2025-12-18T01:24:41-0500

Samu said:
If this is the case, any residue in chemistry is a reason to mix a new batch. C-41 chemistry costs next to nothing compared to film prices, and trying to reuse beyond capacity is basically ruining a $15 film in order to save 50¢. No developer will produce 16 rolls of film per liter unreplenished, if good quality negatives are desired. The main reason for many of the companies catering to hobbyists are claiming unrealistically high capacities of their chemistry, are the low expectations of folks mainly scanning. You can make an acceptable digital scan from a negative which is quite much off the industry standards. But if you print in a darkroom, this is not the case. Bad negatives are hard to woek with, or in the worst case, good results are impossible to achieve. In replenished systems, such as minilabs, filtering the solutions is necessary.

Hie didn´t say he was using a one liter kit. It is possible to use professional chemistry also in tanks or in rotary systems. That said, replenishing is probably not a viable option in this case for C-41 process.

Very well said. Absolutely no reason to overuse C-41. Such false economy. I still print color, it's something that I do rarely, but it's fun. I certainly want everything I can get out of the Ektar and Portra I shoot.

I bought a couple rolls of the Harman Phoenix, I didn't try to print or scan. It's funny looking stuff.

It's whatever you enjoy. Just don't waste valuable film and time on crappy chemistry.

PS the bleach gets reused and replenished, it's almost eternal!

Samu · 2025-12-18T01:28:16-0500

gbroadbridge said:
The entire cohort of Photrio probably comprises less than 0.00001% of the folks using CN film worldwide, so that's not much of an argument

Last time I was in a film lab a couple of weeks ago, the lab operator had not even heard of Photrio.

So no, I'm not exaggerating

Yes, nut for most of people shooting CN, the capacity of chemistry is also irrelevant, because they take their films to commercial lab for developing and printing and/or scanning. What I mean with all of this, is that I would like to know the exact process the OP is using, in order to understand the problem.

koraks · 2025-12-18T03:19:08-0500

Samu said:
I would like to know the exact process the OP is using, in order to understand the problem.

That's always a good starting point, combined with some insight into requirements of expectations in terms of the resulting negatives.

How do you filter your C-41 chemistry?

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How do you filter your C-41 chemistry?

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