Composition
For silver crowns, the grade of silver adhered to the long-standing standard (established in the 12th century by Henry II) – the Sterling Silver standard of 92.5% silver and 7.5% copper. This was a harder-wearing alloy, yet it was still a rather high grade of silver. It went some way towards discouraging the practice of "clipping", though this practice was further discouraged and largely eliminated with the introduction of the milled edge seen on coins today.
In a debasement process which took effect in 1920, the silver content of all British coins was reduced from 92.5% to 50%, with a portion of the remainder consisting of manganese, which caused the coins to tarnish to a very dark colour after they had been in circulation for a significant period. Silver was eliminated altogether in 1947, with the move to a composition of cupro-nickel – except for proof issues, which returned to the pre-1920 92.5% silver composition.
Since standardisation of the UK's silver coinage in 1816 (UK Coinage Reform 1816), a crown has, as a general rule, had a diameter of 38.61 mm, and weighed 28.276g.
Read more about this topic: Crown (British Coin)
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