I have 35mm color negs and 35mm slides exactly the same. Don’t know how that happened. The color negs look sharp. Long ago dont remember telling a lab to create slides from negs or other way around.
Long time ago you could buy a special no-mask negative film to directly convert your color negative into a positive transparend slide.
I’m lost how or when it was done. I don’t shoot with two cameras.
Jim
Something I learned about this year because I often have to identify dupes (duplicates) when organizing the archive I am working on.
There were specific duplicate and reversal films made but sometimes people would just use regular film though it was less suited to it. Looking up the labeling on the film rebates should tell you which is which. Interestingly, they could make larger negatives/positives than the format you originally shot, too. so you could get a frame of any type enlarged to become a 6x? or 4x5 or scaled down onto 35mm, into negative or positive for whatever reason.
For clarity, are the orange base C-41s negative and the clear base slides positive?
This is common and so if this is the case, a typical lab dupe was made. The direction needed changed the process.
Option A:
The original was a color negative (C-41), and the slide is a duplicate
The slide was created by copying a C-41 color negative onto reversal (E-6) slide film. This was done to make slides for projection or references from negative originals. The process required significant color correction to compensate for the orange mask and to invert the negative image. Exposure also had to be carefully controlled, since slide film has far less exposure latitude. This process was more technically demanding and often involved trial and error or specialized lab equipment. Higher end stuff.
Option B:
The original was a color slide (E-6), and the C-41 negative is a duplicate
The negative was created by copying a slide onto color negative film. This was done to make prints from slides using standard C-41/RA-4 printing workflows. It required less color correction than Option A. Exposure needed to be managed to avoid clipping highlights or shadows, but overall the process was easier and more lab-friendly - AKA easier to train people to do this
Differences:
| Direction | Original → Duplicate | Difficulty | Filtering Needed | Purpose |
|---|---|---|---|---|
| C-41 Neg → Slide | Negative → Positive | Harder |  Yes |
Projection, presentation |
| Slide → C-41 Neg | Positive → Negative | Easier |  Sometimes |
Printing, duplication |
Cheers
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That’s great. You can use both with NLP and the slide as a reference for the negative conversion.
Why should yo care? Having a negative and a positive of the same photo is a bonus (see above) you paid for - a long time ago.
It would be interesting to know one way or the other when you’ve established what it is that you’ve actually got, @SSelvidge has covered all the bases. Presumably the slides are mounted individually, how about the colour negatives?
Yes, I used this service in the 1980s and 1990s. I would shoot Kodak C41 and the lab would develop the film, cut and sleeve the negatives, make a set of 4 x 6 prints and a set of 35mm mounted slides. That lab is still in business, but they are no longer offer the slides from color negative film. I never knew how they did it. The date imprint on one of my archived slides was as recent as 2004. I shot a roll of Ilford XP2 black-and-white C41 film and had them make a set of 35mm slides. It was amazing to see those beautiful deep sepia “toned” slides. When I remove the film from the 2 x 2 mount, the sprocket area is transparent with no edge lettering to indicate film stock. You can see a thin black line around the image to indicate it was some sort of duping process. I have a faint memory of the lab advertising the slides from negatives as a revolutionary “Vision” film technology, although I do not think it has anything to do with current ECN-2 stocks.
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