Antique School Slate with Unusually Narrow Frame and Unusually Jointed CornesI consider myself something of a connoisseur of antique school slates at this point, having bought and sold a whole lot of them, and looked at many many more. This one, found in southwest New Hampshire, sold me for the unusual narrowness of the frame, and for its unusual and very sweet notched corner joints. Also, there is a layer of what appears to be iron in between the two layers of the frame. Someone more knowledgable than me can surely understand