Found at the old Coltness Iron Works site, Newmains.
The brick is stamped to the side.
GR’s Dykehead – probably stands for General Refractories. However I am uncertain if it was made by GR in England or at one one the Scottish companies they took over.
GR-Stein Refractories Ltd – Formed by merger in 1970 of John G Stein & Co and General Refractories of Sheffield. GR- Stein became a subsidiary of Hepworth Ceramic Holdings Ltd. General Refractories was formed in 1929. It acquired, amongst others, the Glenboig Union Fireclay Co in 1936, which became its Scottish holding company, and Dykehead Gannister & Fireclay Co of Bonnybridge , George Turnbull & Co of Bonnybridge and Castlecary Brick & Fireclay Co, all in 1936.
Below – A very similar stamp found at the same location.