1916 Great Britain Farthing 1/4 Penny Blackened At Mint NGC VF 20 Brown King Gregory V
Obverse:Head Left Reverse:Britannia seated right
in 1897, The United Kingdom started blackening Farthings because of
their resemblance to the Gold Half Sovereign. An acid gas, sodium thiosulphat, was used to color the coin, this process lasted until 1917.