Question: when did they start adding zinc to pennies
[{'answer': '1864', 'provenance': [{'wikipedia_id': '164092', 'title': 'Penny (United States coin)', 'start_paragraph_id': 68, 'start_character': 138, 'end_paragraph_id': 68, 'end_character': 142, 'bleu_score': 1.0, 'section': 'Section::::Lincoln cent.:History.:Composition.\n'}]}, {'answer': '1943', 'provenance': [{'wikipedia_id': '164092', 'title': 'Penny (United States coin)', 'start_paragraph_id': 6, 'start_character': 3, 'end_paragraph_id': 6, 'end_character': 7, 'bleu_score': 1.0, 'section': 'Section::::History of composition.\n'}]}, {'answer': '1864 -- 1942'}, {'provenance': [{'wikipedia_id': '164092', 'title': 'Penny (United States coin)', 'start_paragraph_id': 6, 'start_character': 0, 'end_paragraph_id': 6, 'end_character': 471, 'bleu_score': 0.9163801224442231, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4112214884383994145}, 'section': 'Section::::History of composition.\n'}]}, {'provenance': [{'wikipedia_id': '167436', 'title': '1943 steel cent', 'section': 'Section::::Abstract.', 'start_paragraph_id': 1, 'end_paragraph_id': 1, 'meta': {'evidence_span': ['1943 steel cents are U.S. one-cent coins that were struck in steel due to wartime shortages of copper. The Philadelphia, Denver, and San Francisco mints each produced these 1943 Lincoln cents. The unique composition of the coin (low-grade steel coated with zinc, instead of the previously 95%-copper-based bronze composition) has led to various nicknames, such as "wartime cent", "steel war penny", and "steelie". The 1943 steel cent features the same Victor David Brenner design for the Lincoln cent which had been in use since the first in 1909.', '1943 steel cents are U.S. one-cent coins that were struck in steel due to wartime shortages of copper. The Philadelphia, Denver, and San Francisco mints each produced these 1943 Lincoln cents. The unique composition of the coin (low-grade steel coated with zinc, instead of the previously 95%-copper-based bronze composition) has led to various nicknames, such as "wartime cent", "steel war penny", and "steelie". The 1943 steel cent features the same Victor David Brenner design for the Lincoln cent which had been in use since the first in 1909.', 'The 1943 steel cent features the same Victor David Brenner design for the Lincoln cent which had been in use since the first in 1909.']}}]}, {'provenance': [{'wikipedia_id': '2221172', 'title': 'Indian Head cent', 'section': 'Section::::Production.:Shortage and redesign (1862–1864).\n', 'start_paragraph_id': 26, 'end_paragraph_id': 26, 'meta': {'evidence_span': ['The legislation passed the House, and the Coinage Act of 1864 was signed by President Abraham Lincoln on April\xa022, 1864. The legislation made base metal coins legal tender for the first time: both cents and two-cent pieces were acceptable in quantities of up to ten.', 'The legislation passed the House, and the Coinage Act of 1864 was signed by President Abraham Lincoln on April\xa022, 1864. The legislation made base metal coins legal tender for the first time: both cents and two-cent pieces were acceptable in quantities of up to ten. The government would not, however, redeem them in bulk. The act also outlawed the private one- and two-cent tokens, and later that year Congress abolished all such issues. The legislation did not allow for the redemption of the old copper-nickel cents; it had been drafted by Pollock, who was hoping that the seignorage income from issuing the new coins would help finance Mint operations, and he did not want it reduced by the recall of the old pieces. Wharton and his interests were appeased by the passage of a bill for a three-cent piece in 1865 and a five-cent piece in 1866, both of his proposed alloy, out of which the "nickel", as the latter coin has come to be known, is still struck. Despite this, Wharton and his nickel interests made repeated attempts to return nickel to the cent, each time failing, both as part of the deliberations over what became the Coinage Act of 1873, and in the early 1880s. The copper-nickel cents from early in 1864 were generally bought up by speculators and did not circulate in large numbers. The Mint began producing bronze cents on May 13,', 'The legislation made base metal coins legal tender for the first time: both cents and two-cent pieces were acceptable in quantities of up to ten. The government would not, however, redeem them in bulk.']}}]}]