This early example dry process and embossed BOCH INSULATOR PAT APLD FOR and is a three part glaze weld.  These were actually glaze filled insulators as they added significantly more glaze than necessary to just hold the pieces together to improve the insulation value.

The later and more common Boch patent styles are wet process and are most common in white but can be found with brown glaze.  These are incuse marked BOCH PATENT / MARCH 22, 1898 / MF'D BY / THE R. THOMAS AND SON'S CO.  (US Patent 601,195)