1917 Halfcrown

[Peckris 579]

23 hours ago, ozjohn said:

A poor choice of metals to replace sterling silver perhaps. They did not hit on the right alloy until about 1927.I think I remember that the early 50% silver coins were "treated"to migrate Ag to the surface to improve their appearance. This can be seen when they wear and take on a distinct "coppery"look. Even with the increased copper in these coins I have never seen green verdigris form on these coins even when they have been lying forgotten in a draw for years. In Australia, where these coins were stored we experience much higher humidity than the UK which is conducive to the formation of verdigris. No verdigris was found on these coins.

No, that was the second or third attempt, after awful yellowing even on virtually Unc specimens. Certainly by 1925 they were doing what you said, which is why worn 1925 halfcrowns have those ugly brown patches.

[ozjohn 552]

Sorry, I think you are right. Thinking back the 1920 - 1922 were not too bad with regards to the alloy color but the strike quality was poor perhaps due to the hardness of the alloy even with the recut effigy. The poor copper color was as you say 1924 -25 and by 1927 they got the alloy right.