Gunk on Negatives

[ChristopherMarv]

The depressing quest for a daylight processing solution for 5x7 continues.

I tried using this reel from 20th Century Camera:

https://20thcenturycamera.com/collec...et-film-reel-1

Notice that it has a retainer for each sheet at the center. I also bought a very similar reel from the Film Photography Project, and it seems to be the same product, but a different color and branding:

https://filmphotographystore.com/col...reel-reel-only

I developed a negative in the 20th Century Camera reel, but was left with a narrow line of gunk on the non-emulsion side of the negative, corresponding to the position of the middle retainer on the reel. I tried to clean it off when the negative was still wet, but it just flattened and now appears like this:



I had an e-mail exchange last night with a polite gentleman from 20th Century Camera who offered to send me a new reel, even after I confessed that I had ruined the first one by rinsing with excessively hot water (contrary to the instructions).

I then developed a second sheet with the Film Photography Project reel, and had a similar problem, although it is less pronounced and difficult to get a good photo of:

I washed the Film Photography Project Reel with dish soap before using, cleaning the inside of each center retainer with a q-tip. Anyone know what this gunk is, or how to remove it?

Thank you.