Title: History of the British penny (1901–1970)
Content:  percent zinc. Such coins tarnish to a colour different than the prewar coins, and they were treated with sodium thiosulphate to give them a darker tone. That substance, dubbed "hypo", had been used to darken all 1934 pennies before issue and most of the 1935 mintage, "Hypo" would be used again in 1946, discolouring the coins to discourage the hoarding of new pennies. Although the prewar alloy was restored in 1945, the Mint reversed itself in 1959, made pennies out of that wartime composition for the remainder of the coin's pre-decimal history without chemical treatment, and continued its use for the new decimal bronze pieces. By the late 1940s, demand for pennies was 
Title: Zinc
Content:  In 1982, the US Mint began minting pennies coated in copper but containing primarily zinc. Zinc pennies pose a risk of zinc toxicosis, which can be fatal. One reported case of chronic ingestion of 425 pennies (over 1 kg of zinc) resulted in death due to gastrointestinal bacterial and fungal sepsis. Another patient who ingested 12 grams of zinc showed only lethargy and ataxia (gross lack of coordination of muscle movements). Several other cases have been reported of humans suffering zinc intoxication by the ingestion of zinc coins. Pennies and other small coins are sometimes ingested by dogs, requiring veterinary removal of the foreign objects. The zinc content of some coins can cause zinc toxicity, commonly fatal in dogs through severe hemolytic anemia and liver or kidney damage; vomiting and diarrhea are possible symptoms. Zinc is highly toxic in parrots and poisoning can often be fatal. The consumption of fruit juices stored in galvanized cans has resulted in mass parrot poisonings with zinc.
Title: Penny debate in the United States
Content:  of about  cents. After 1857, the new smallest coin was the one-cent, which had a -equivalent buying power of  cents. The nickel fell below that value in 1973; the dime (at 10 cents) fell below that value in 1981; the quarter (at 25 cents) fell below that value in 2012. ; Zinc toxicity – Zinc can cause anemia or gastric ulceration in babies that inadvertently ingest pennies made after 1982. A single penny can kill a pet. ; Environmental hazard – The mining of zinc and copper causes toxic pollution and is especially undesirable when considering the valuable metals being used to produce a coin with 
Title: Zinc
Content:  one cent coins (pennies) since 1982. The zinc core is coated with a thin layer of copper to give the appearance of a copper coin. In 1994, 33200 t of zinc were used to produce 13.6 billion pennies in the United States. Alloys of zinc with small amounts of copper, aluminium, and magnesium are useful in die casting as well as spin casting, especially in the automotive, electrical, and hardware industries. These alloys are marketed under the name Zamak. An example of this is zinc aluminium. The low melting point together with the low viscosity of the alloy makes possible the production of small and intricate shapes. The low working temperature leads 
Title: Penny (United States coin)
Content:  The composition of the penny has varied over time: The isotope composition of early coins spanning the period 1828 to 1843 reflects the copper from Cornish ores from England, while coins after 1850 reflect the Keweenaw Peninsula, Michigan ores, a finding consistent with historical records. In 1943, at the peak of World War II, zinc-coated steel cents were made for a short time because of war demands for copper. A few copper cents from 1943 were produced from 1942 planchets remaining in the bins. Similarly, some 1944 steel cents have been confirmed. From 1944 to 1946, salvaged ammunition shells made 
Title: Coin
Content:  each penny. Since mid-1982, United States pennies are made of 97.5% zinc, with the remaining 2.5% being a coating of copper. Extreme differences between fiat values and metal values of coins cause coins to be hoarded or removed from circulation by illicit smelters in order to realize the value of their metal content. This is an example of Gresham's law. The United States Mint, in an attempt to avoid this, implemented new interim rules on December 14, 2006, subject to public comment for 30 days, which criminalized the melting and export of pennies and nickels. Violators can be fined up to $10,000 and/or imprisoned for up to five years.
Title: Penny (United States coin)
Content:  Zinc, a major component of U.S. cents minted after mid-1982, is toxic in large quantities. Swallowing such a coin, which is 97.5% zinc, can cause damage to the stomach lining because of the high solubility of the zinc ion in the acidic stomach. Coins are the most commonly ingested foreign body in children but generally are allowed to pass spontaneously unless the patient is symptomatic. Zinc toxicity, mostly in the form of the ingestion of U.S. pennies minted after 1982, is commonly fatal in dogs where it causes a severe hemolytic anemia. It is also highly toxic in pet parrots and can often be fatal.
Title: Penny (British pre-decimal coin)
Content:  of George VI's reign: None were minted in 1941, 1942 and 1943. Pennies minted in 1950 and 1951 were for overseas use only. One 1952 penny, believed to be unique, was struck by the Royal Mint. The worldwide shortage of tin during the Second World War caused a change in the alloy in 1944 to 97% copper, 0.5% tin, 2.5% zinc, but this bronze tarnishes unattractively, and the original 95.5% copper, 3% tin, 1.5% zinc alloy was restored in 1945. Because of the large number of pennies in circulation there was no need to produce any more in the 1950s, however 
Title: Penny (British pre-decimal coin)
Content:  large number of specimen sets were issued in 1953 for Elizabeth II's Coronation. At least one 1954 penny was struck, apparently for private internal purposes at the Royal Mint, but it was not until 1961 that there was a need for more pennies to be minted, and production continued each year until 1967, and afterwards (as pennies continued to be minted with the date 1967 until 1970). The 97% copper, 0.5% tin, 2.5% zinc alloy was used again for the 1960s pennies. Finally, there was an issue of proof quality coins dated 1970 produced to bid farewell to the denomination.
Title: History of the British penny (1901–1970)
Content:  coin was struck at a loss; the Mint hoped for a reduction in size, and the demonetisation of the farthing at the end of 1960 helped clear the way for such a scheme. It was not until 1961 that there was a need for more pennies to be minted, and production continued each year in very large numbers until the final pre-decimal pennies for circulation, dated 1967, were coined. The old bronze penny was slated for elimination as decimal currency was planned in the 1960s. It continued to be struck after 1967, still bearing that date. The 97 percent copper, 0.5 percent tin, 2.5 percent zinc alloy was used again for the 1960s pennies. Finally, there was an issue of 

Question: when did they start adding zinc to pennies?
Answer: 1864.
1943.
1864–1942.