Hi Kent,

It's possible. There was once a place in Seattle (can't recall the name) that sold cine (movie) film loaded into 35mm cassettes, which you'd shoot, mail to them and receive negatives, prints and slides in return. The trifecta!

Perhaps dad was using them, or somebody similar?

As follow-up to slides vs. color negatives, slide film generally has better (more accurate) color response under the intended light but is more demanding of exposure (less latitude) and more contrasty than negative film. Color print film has a lot more leeway in exposure and color temperature.

The printing process covers a good deal of negative film exposure errors, while slides are strictly WYSIWYG. It's also trickier to print from slides, as you need either a direct-positive print by a custom lab (expensive) or an internegative, which means every print is third generation.

I suspect most custom labs do high rez scans and print digitally, today. The darkroom "wet side" is essentially kaput, other than B&W.

Cheers,