George III 1760-1820 AD

The guineas of King George III weighed 8.4 g and were 24 mm in diameter, with an average gold purity (at the time of the 1773 assay) of 0.9146 (meaning it contained 7.7 g of gold). They were issued with six different obverses and three reverses in 1761, 1763-79, 1781-99, and 1813. All the obverses show right-facing busts of the king with the legend GEORGIVS III DEI GRATIA with different portraits of the king. The reverse of guineas issued between 1761 and 1786 show a crowned shield bearing the arms of England+Scotland, France, Ireland and Hanover, with the legend M B F ET H REX F D B ET L D S R I A T ET E date ("King of Great Britain, France and Ireland, Defender of the Faith, Duke of Brunswick and Lüneburg, Arch-Treasurer and Elector of the Holy Roman Empire"). In 1787 a new design of reverse featuring a spade-shaped shield was introduced, with the same legend; this has become known as the spade guinea.

In 1774 almost 20 million worn guineas of King William III and Queen Anne were melted down and recoined as guineas and half-guineas.

Towards the end of the century gold began to become scarce and rise in value. The French Revolution and the subsequent French Revolutionary Wars had drained gold reserves and people started hoarding coins. Parliament passed a law making banknotes legal tender in any amount, and in 1799 the production of guineas was halted, although half- and third-guineas continued to be struck. Following the Act of Union between Great Britain and Ireland in 1800, the king's titles changed, and an Order in Council of 5 November 1800 directed the Master of the Mint to prepare a new coinage, but although designs were prepared, the production of guineas was not authorised.