Here are a couple of ideas
- apply the black and white treatment to the scans of black and white film
- apply a keyword to these scans of black and white film
Yes. Could do either of those, but that would entail going through several thousand photos and tagging them / editing them. I was trying to avoid doing that.
But as far as I know, every search method in Lightroom depends on metadata being present, and for these scanned black and white photos, there is no such metadata indicating it is black and white.
Well, yes, you are correct. However, I was wondering if there was something in the file format and that was exposed to Lr that could indicate it was black and white rather than colour.
It seems probably not.
Is the particular scanner used stored in the metadata of the file? I don't know. You could use something like ExifTool to examine all of the metadata associated with these black and white photos. That could narrow it down some, eliminating photos taken by digital cameras or from other capture devices.
Do keep in mind that there is really nothing in the files to indicate they are black & white, except your interpretation of them.
Lightroom's "B&W" conversion leaves a marker in the XML develop history, which wouldn't be there for scans. It's that marker that you are currently using for your smart collection.
But, for scans and Documents that perhaps were converted to B&W outside of LR (such as a color image processed with Silver Efex Pro), there is no such marker. In fact, these images are all RGB color images. You can't even check for the presence of color pixels, because often "B&W" images are tinted with sepia or blue colors to add antique effects.
So, at the end of the day, there really isn't any automated process you could use.
However, there's a quick way to apply keywords to your images (you could also use it to apply the B&W treatment) - you can use the spray paint can in LR. Set your grid view to relatively small, and you can scan your folders and spray with the paint can to apply a B&W preset or to apply keywords.
This may be the fastest way. I'd be inclined to use a keyword, as I'd be afraid of changing the appearance of my images with a B&W treatment.