Weird blotches on old negatives and slides?

Question

I am scanning some of my old negatives and slides. On some I have found a weird blotching, almost like a fungus that is growing on one side of the slide/negative (I've found the same on both media). It is really obvious and seems to be on the shiny (?) side, it is easily observable from several feet away without holding up to the light when looking at that side of the negative, but cannot see from the other side until you hold it up to the light and look closely. I'm not talking about little splotches, these are big and all over the negative/slide, essentially ruining them. See attached photo.

Any idea what this is? I am assuming these are not salvageable. These have been in archival preserver sheets in a binder for decades.

Answer 1

This looks like mould on your slides. It's fairly common, unfortunately, and it appears the preserver sheets were unable to stop this from growing.

You could of course try cleaning the slides. There is always a chance the mould has yet to permanently damage the film, and if it hasn't yet it will sooner or later. Cleaning the slides now could prevent that from happening.

I found this guide to cleaning mould from slides:

1. Moisten the photo chamois/pad/cotton with the isopropyl alcohol, and gently wipe the film until it is clean.
2. Remount the slides in clean glass mounts or new cardboard mounts.

Make sure to wear (cotton) gloves, and store the film in a dry area so new mould will have a smaller chance of growing.