Whiteboard
Whiteboards became commercially available in the early 1960s, but did not become widely used until 30 years later. Early whiteboards needed to be wiped with a damp cloth and markers had a tendency to leave marks behind, even after erasing the board. Dry-erase markers for whiteboards were invented in 1975.
Wobble board
Official Rolf Harris wobble boards were sold commercially for a time in the 1970s but most are made by the player. Almost any large, springy and flexible sheet of material can be used as an impromptu wobble board, although some materials are markedly better than others. Harris's instrument was originally made from a type of wood composite known as hardboard (Masonite in the United States and Australia). According to an interview he gave to Tony Barrell for "The Sunday Times Magazine" in 2001, Harris discovered the musical properties of hardboard by chance in 1959, when he was about to paint a portrait of the conjurer Robert Harbin. Before his subject arrived, Harris prepared the background, covering a large piece of hardboard with Prussian blue oil paint mixed with turpentine. But the surface refused to dry. "It was all sticky and nasty. He was due to arrive in about half an hour." In desperation, Harris propped the board over a paraffin heater. When he touched it later, it was so hot it burned his finger. "So I propped it between the palms of my hands and shook it to cool it down. And ... I thought, 'What a marvellous sound.'"