The golden bay colt Radium was by Bend Or and he was grand sire of the famous Australian racehorse Phar Lap. His successes included winning both the Goodwood Cup and the Doncaster Cup in 1908, and the Jockey Club Cup in both 1907 and 1908. These were weight for age races, meaning that entries could be horses of any age, but the older and more experienced horses carried more weight than the two or three year olds.
The present watercolour is either a study for, or a later version of, the oil Thoroughbred Stallion "Radium" destoyed by enemy bombing in World War II, which had been painted circa 1921-22 at Southcourt Stud for Anthony de Rothschild (see Sir A. Munnings, Pictures of Horses and English Life, London, 1927, pl.IV and between pp.96 and 97 of The Second Burst, 1951). It was exhibited at the Royal Academy in 1923, no.233.
In the Daily Telegraph's review of the Royal Society of Painters in Watercolour exhibition (4 November 1944), the present watercolour of Radium was described as a 'spirited and attractive performance'. Watercolour was a relatively rare medium for Munnings who gave it up from the mid-1920s due to the difficulty of transporting all the neccesary equipment.
Munnings described the time he spent at Southcourt Stud '... how I have enjoyed painting this picture or that, but never have I enjoyed painting pictures more than those of brood mares, foals and stallions, how and when I liked, as I did at the Southcourt Stud'. In particular, Radium stood out, 'a golden bay with a fine arab head, black points, long black mane and a tail like a plume!'. After the war, when Munnings learnt the fate of the destroyed oil painting, he wrote that it was the 'hardest blow I have ever known' (see Sir A. Munnings, op. cit. p.91).
Radium died in 1923. When the authors of the Lonsdale Library edition on flat racing (published some fifteen years later) looked for a picture to show the perfect thoroughbred head, they picked a photograph of Radium's head as being about 'the handsomest and most typical of the breed'.