Johan Willem Frederiks worked for the Ministry of Agriculture, Industry and Trade and in his spare time was a passionate collector of old arts and crafts, from the Middle Ages to the 18th century.
He later widened the scope of his collection to include Renaissance bronzes and 15th- and 16th-century paintings. Like Bierens de Haan, Frederiks became an expert in his sphere of collecting alongside his daily activities.
Frederiks published on his collection and loaned items from it for exhibitions. When he sold parts of his collection to museums, Museum Boymans also benefited, for example with the purchase of his collection of ornamental pewter. After his death his daughter gave important parts of the collection on loan to the museum; these were later converted into a gift.