While scanning many 35 mm slides (mostly Kodachrome and its successors, i.e. Kodachrome II and 64), I noticed what appear to be pinholes in the emulsion, perhaps on the order of 10 or 100 microns. The defects are mostly from some slides, taken in the U.S. Southwest in the late 1980's, such as that below, cropped from a photo in Bryce Canyon National Park in Utah. Others, from other places, even taken on the same roll, do not have pinhole defects, or just one or two occasional defects on a slide.

Bryce Canyon with pinholes

The defects are the tiny white dots visible against the dark background to the right.

Though I can think of alternative causes, such as electrostatic discharge (unlikely, as it was in summer, and there are no accompanying streaks) or scratches (however, they're points, not linear), I thought [the defects might be due to radiation from past nuclear weapons testing upwind from that area, either alpha particles, or judging by the comparatively size, even fission fragments. Contaminated dust certainly could have entered the camera while changing lenses or film. Plain dust itself is unlikely to have caused the issue, since Kodachrome is a reversal film, and that would have left dark spots.

Does anyone have insight into what may have caused the pinholes? Is nuclear radiation damage an actual likelihood, or is that farfetched?

  • \$\begingroup\$ What specific film were you using at the time? Were you using the same film with slides made before and after the ones with holes? Did the manufacturer of that specific film make any significant changes to the emulsion around the time the holes started appearing or stopped appearing? \$\endgroup\$
    – Michael C
    Jan 4, 2021 at 17:12
  • \$\begingroup\$ As mentioned, Kodachrome (or K II) was used for these shots, and development of Kodachrome was only done by Eastman Kodak, AFAIK, because of its unforgiving chemistry. And, on the same roll, some slides have spots and others don't. \$\endgroup\$ Jan 4, 2021 at 18:33
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    \$\begingroup\$ Kodachrome was offered in more than one speed/specific emulsion. If some frames have the spots and some don't, I doubt it's radioactive dust since dust can get onto film when it's on the takeup spool just as easily as when it's behind the shutter or being exposed. Once dust is inside the film chamber it can wind up pretty much anywhere within the film chamber. \$\endgroup\$
    – Michael C
    Jan 4, 2021 at 18:44
  • \$\begingroup\$ Have you inspected the actual slides with a loupe to determine if the small spots are actually visible on the slides, or might instead be an artifact of the digital conversion? \$\endgroup\$
    – Michael C
    Jan 4, 2021 at 18:46
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    \$\begingroup\$ After the mid-1960s, Kodachrome was processed by more than one lab -- in fact, the very last place on Earth to get K-14 film processed was a private lab. Dark halos around white spots suggests holes in the gelatin, which is likely due to poor storage conditions. \$\endgroup\$
    – Zeiss Ikon
    Jan 4, 2021 at 19:22

1 Answer 1


The processed Kodachrome slide film consists of colored dye imbedded in purified gelatin. If you examine a slide via reflected light, looking at the emulsion side, you will see relief image. Meaning the slide is not uniformly flat, the gelatin had different thicknesses based on image content.

The gelatin of the emulsion is an attractive food for microscopic beasties. These arrive and land on the film as airborne spores. The gelatin emulsion is hydroscopic and quickly gains water from damp air. In other words, all the ingredients needed for besties is present.

Kodak applied a coat of lacquer to seal the emulsion, other photofinishers did this on a hit or miss basis. Additionally the film was treated with a biocide. Over time the biocide out-gasses. Sorry for your loss - my lab 3M Dynacolor applied the lacquer.


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