Antique Stanley Gibbons 391 Strand Ceramic Watermark Detector Tray Boxed Manual Title: Vintage Stanley Gibbons 391 Strand Black Ceramic Watermark Detector Tray Boxed Description: Genuine antique/vintage Stanley Gibbons Ltd. (391 Strand, London) black glazed ceramic watermark detector tile, complete with its original box and instruction leaflet. • Dimensions: Approx. 77.2mm x 77.2mm (3 inches square) x 11.5mm thick. • Condition: Clean and appears unused. The glossy black glaze is free of tweezer