Anybody know what this is?

[mccolalx]

Seems to be some kind of contact printing frame or plate holder, but I'm not sure how it's used. Fancier than any I've ever seen...

[mccolalx]

last photos, showing the one marking on it

[BrianShaw]

I'd guess a plate holder.

What are the dimensions?

[mccolalx]

the glass in it is 11 3/4" x 9 3/4"

[mccolalx]

the darkslide is also hinged in 2 places, which i've never seen before in a holder

[E. von Hoegh]

the darkslide is also hinged in 2 places, which i've never seen before in a holder

I'm speculating, but that would allow it to hang down (in vertical orientation) rather than stick up or out as a wind vane.

[BrianShaw]

I have a bunch of smaller plate holders from British plate cameras that are hinged like that. Mine slide in/out and are two-sided so they don't have the cool-looking spring clamps like yours does.

[E. von Hoegh]

I wonder if it is a plateholder designed to double as a contact frame?

[mccolalx]

Thanks for the help...it's definitely the prettiest, most overengineered holder I've ever seen

[BrianShaw]

I suspect that would make a cool printing frame if you are into alt printing.