Late hollow zinc FCL.
I agree with Janos, this one is attributed to the firm of Franke & Co., Lüdenscheid. It is a silver grade with sheet metal hinge and a "?" style catch. These came with a white frosted type finish that did not hold up well over time. It did however adhere to the exposed solder around the catch; a trait often found on these hollows.
FCL made both hollow and solid IAB's. The hollows are found with both a sheet metal and block hinges. The unmarked solids used the small block hinge and a maker marked example that came with crimped in hardware.
Best Regards, fischer
Thanks for help!