'It seems to me absurd to live in an age of flying and yet not be able to execute tonal glides and curves - just as absurd as it would be to have to paint a portrait in little squares (as in the case of mosaic) and not be able to use every type of curved lines.' Percy Grainger, Free Music, 6 December, 1938

An accomplished visual artist and highly analytical thinker, Grainger documented his Free Music experiments extensively and in great detail. His daybooks contain detailed accounts of the progress of individual experiments, as he worked through ideas with his collaborators Burnett Cross and Ella Grainger. Particularly successful experiments were marked in the daybooks as 'Red Letter Days'.

The illustrations of his Free Music experimentation, some of which are shown below,  show an innovative approach to documentary practice. These illustrations inhabite a middle ground between scientific accounts and aesthetically rewarding artwork. These documents reflect his desire to make ‘pretty machines’ that were at once both visually exciting and mechanically functional.