What causes tiny white pinholes on scanned Kodachrome 35mm slides?
Asked 1/3/2021
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While scanning older 35mm Kodachrome slides, I’m seeing clusters of tiny white dots in dark areas of some frames. They look like pinholes in the emulsion, roughly tens of microns across. The issue appears on some slides from the late 1980s, while other slides from the same era—or even the same roll—show few or none.
What is the most likely cause of these tiny white spots on Kodachrome slides? Could they be emulsion damage, fungal/microbial attack, dust, static, or something else? Is radiation damage a realistic explanation, or is that unlikely?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
5y ago
2 Answers
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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.
Originally by user44949. Source · Licensed CC BY-SA 4.0
user44949
5y ago
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Generated from our catalog & community — verify before relying on it.
The most likely cause is deterioration of the slide’s gelatin emulsion, often from fungal or microbial attack, not radiation.
Processed Kodachrome contains dyes embedded in a purified gelatin layer. That gelatin can absorb moisture from humid air, and airborne spores can settle on it. Over time, if the protective lacquer/seal is incomplete or aging, and as the film’s biocide protection fades, microscopic biological damage can occur. This can leave tiny spot-like defects that scan as white dots, especially visible in dark image areas.
That explanation fits better than dust, scratches, or static:
- dust on reversal film would more often appear dark, not white
- scratches are usually linear
- static discharge typically produces branching or streak-like marks, not isolated pinholes
Radiation from fallout is highly unlikely as the cause. The pattern and rarity on only some slides are much more consistent with age/storage-related emulsion damage than with nuclear radiation exposure.
If the slides are important, handle them carefully and store them cool and dry to slow further damage.
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