I've just been examining my collection of 35 mm colour positive slides and I have noticed something unusual. The edge of the colour positive slide, where the image meets the inner rim of the border it is housed in, is a lighter shade compared to the rest of the picture. In some slides it may be the bottom edge and the right side of the image. In other slides it may be all four edges.

Does anyone know why this is?

Additional information: The lighter borders are only visible when viewing the slides over a dark area. In normal light the slides look perfectly normal.

  • \$\begingroup\$ Hi Stan, They are colour positive slides. I have edited my post to reflect this. By examining the slides, they appear to meet a black border. Hope this helps. \$\endgroup\$ Feb 13, 2018 at 15:16
  • \$\begingroup\$ Are your slides stored in a tray, in plastic pages, or in a cardboard or plastic box? "The inner rim of the border it is housed in"… Are they mounted in cardboard, plastic, or metal? Are they in glass? Do you see any specific tint to the lighter edges, bluish or yellowish, say? \$\endgroup\$
    – Stan
    Feb 13, 2018 at 16:31
  • \$\begingroup\$ I did keep the slides in plastic sheets, but then transferred them to a box. The mounts are all made of plastic. I don't see any specific tint to the lighter edges except possibly yellowish. Hope this is useful. \$\endgroup\$ Feb 13, 2018 at 16:41
  • \$\begingroup\$ I suspect something happened since you first observed them and that they changed over some time. Do you have any slides from the same era still in slide pages to compare with those you boxed? Try to find what may be common among the affected ones among your collection—or are all of your slides affected? \$\endgroup\$
    – Stan
    Feb 13, 2018 at 17:06
  • 1
    \$\begingroup\$ It would be great if you could add an image to your question. \$\endgroup\$ Feb 15, 2018 at 14:27

1 Answer 1


Your slides are most likely duplicates. The white borders are where some light leaked through the dark borders surrounding the image in the original film. Duplication is performed by bringing the unexposed slide film's emulsion directly into contact with the exposed slide film's emulsion and "flashing" the image onto the dupe.

To learn more about "vintage" slide duplication techniques you could check out manuals for those devices. Beseler dual mode slide duplicator - A camera based duplicator Polaroid Polaprinter - Duplicated slides onto Polaroid

It is also possible that this is a form of in-camera masking. White-light masking is very rare and generally only used in scientific devices.

An even less likely explanation is that your slides are negative duplicates of a negative (two negatives makes a positive.) If that were true, though, you would have likely figured it out since the borders would have the characteristic beige base+fog of a normal color negative. This has, to my knowledge, never been common practice but it is possible using the technique mentioned above.

  • \$\begingroup\$ Thanks for your feedback on this issue. Can I ask where you got this information from regarding how duplication is performed? I'd like to do more research. \$\endgroup\$ Feb 14, 2018 at 16:03
  • \$\begingroup\$ Added a few resources to the answer \$\endgroup\$ Feb 15, 2018 at 18:56
  • \$\begingroup\$ I think this is an excellent answer, very interesting. \$\endgroup\$ Feb 18, 2018 at 18:36

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