Willem van de Velde Jnr was born in Holland in 1633, son of Willem Snr (an artist) and brother to Adrian (also an artist). He spent much of his working life in Greenwich, London, and is buried in St James’ Church, Piccadilly.
He was particularly known for sea and marine paintings, like the one shown above which was hanging in the National Gallery of South Africa at the time this stamp was produced.
https://en.wikipedia.org/wiki/Willem_van_de_Velde_the_Younger
The South Africa National Gallery moved into its current home in 1930 – it looks like a fabulous bit of architecture. You can explore the collections of the South Africa National Gallery at:
https://www.iziko.org.za/collections
Stamp of the Day 