Source, in full
Quote of Mondrian, 1930 reacting on Alexander Calder, as cited by by Mondrian's recent biographer Hans Janssen, of the Gemeentemuseum in The Hague; as cited by Alastair Sooke, in 'Mondrian - the Joy of Being Square'; BBC culture, 10 July 2017
Notes from Wikiquote
In 1930, the American sculptor Alexander Calder, (inventor of the mobile
moving sculpture) visited Mondrian in his studio in Paris. Calder said 'Maybe you should take all these red, yellow and blue elements off the canvas and let them hang in the air, so they can move'.