Dear Peter
I am writing to you in response to your enquiry of 25 April.
The Deputy Master of the Royal Mint wrote the following in his Annual Report of 1934 about the darkening of pennies:
“In my Report for 1933 I drew attention to the fact that no bronze pennies were required to be struck for circulation in that year. Large stocks of this denomination were held by the Banks and, in accordance with the usual policy of this Department, the issue of pence had from October, 1932, been suspended in this country. In the autumn of 1934, however, it became evident that the stocks had to a large extent been absorbed. I, therefore, invited representatives of the Banks to meet me in order to discuss this position. As a result of our deliberations it was generally agreed that the ban on the issue of new pennies from the Mint should be to some extent relaxed. There was, however, some anxiety displayed that the issues should not be too lavish, especially in meeting the constant demand for bright new pennies, so much desired for the Christmas Stocking, a demand which is spurious to the extent that it is followed, as it often is, by inconvenience to the Banks when the young recipients disgorge their treasures in exchange for other delights which subsequently appeal still more to their taste. Last Christmas, therefore, I felt compelled to meet these views of the Bankers and arranged that all new pence, for the time being, should be issued only after their attractive sheen had first been removed. I am glad to be able to report that, in view of the clear evidence we now have of a very large increase in the genuine demand for pennies this year, the precaution has not proved necessary.”
I hope this answers your question.
Best wishes