A mark applied to glass and ceramic wares from 1842 to 1883 This mark and the numerals / numbers / letters incorporated in it indicated that the design had been registered with the Patent Office An item may have carried the mark for many years after its initial registration date thus making the mark an unreliable dating method The South African digger / collector will be fortunate to find anything bearing a diamond registration mark other thyan the "Square Top" red ink bottle pictured as diamond registration marks were replaced with registration numbers after 1884 This system is fully explained on pg 18,19 of Bottles & Bygones click to view diamond registration