by uthminsta » Sat Jan 22, 2011 11:33 pm
Here's a timeline of what I know. The transition came during 1982:
Timeline of the 1982 cent
All mints began the year producing large date cents.
January 7: West Point mints zinc cents from the start. Total WP mintage 1,990,005,000. No mint mark.
Soon after, Philadelphia switched from copper to zinc.
Total Phila mintage 7,135,275,000. Nearly 600 million per month, or 19.5 million a day.
San Francisco mint 1,587,245,000 zinc cents for circulation. No mint mark.
San Francisco (S) also struck nearly 4,000,000 proof cents, all large date and copper.
September 3: all mints switch to small dates.
October 21: Denver switched from copper to zinc.
October 27: first Denver zinc cents are delivered.
Total Denver mintage: 6,012,979,368. Assumed production of 1-1.2 billion Denver zinc small dates.
On the copper-to-zinc switchover days, production stopped completely, they cleared the production floor of all planchets, then they started with zinc. If there are any 1983 copper cents, it's quite possible the copper planchets were saved by mint workers, and purposely fed into the press in order to purposely create a rarity.
Now I'm not sure about this, but I do believe the 1983 PROOF cents were still copper because they hadn't figured out yet how to keep the copper plating from cracking under the higher-pressure striking necessary for proof coins. Someone else may have to verify that statement.