Recognized as one of the finest painters ever born in the Hague, Koster worked throughout Holland, Germany and England during his career. Led to each country to study in their finest academies, he gaining acclaim amongst his peers and professors. Yet always he returned home to the north coast of the Hague and the town of Scheveningen.
His exacting style hip H.M.D. CONWAY; he also served the R.N.V.R. and as commissioned naval artist in the first world war. (From this period's work, mason contributed fifty-six of his paintings to the imperial war museum.)
With continual access to the ships of the world, mason centered himself in the community of Ebbertson Hall in Yorkshire along the northeastern coast of England near the major port of Liverpool.