An Oak Tree is a conceptual work of art created by Michael Craig-Martin (born 1941) in 1973. The piece, described as an oak tree, is installed in two units – a pristine installation of a glass of water on a glass shelf on metal brackets 253 centimetres above the ground, and a text mounted on the wall. When first exhibited, the text was given as a handout. The text takes the form of a Q&A about the artwork, in which Craig-Martin describes changing "a glass of water into a full-grown oak tree without altering the accidents of the glass of water," and explains that "the actual oak tree is physically present but in the form of the glass of water." Craig-Martin considered "the work of art in such a way as to reveal its single basic and essential element, belief that is the confident faith of the artist in his capacity to speak and the willing faith of the viewer in accepting what he has to say". The Catholic Herald compared the work to the Roman Catholic doctrine of Transubstantiation and the Real Presence. The original is in the National Gallery of Australia, and an artist's copy is on loan to the Tate gallery. Artwork An Oak Tree is a work of art created by Michael Craig-Martin in 1973, and is now exhibited with the accompanying text, originally issued as a leaflet. The text is in red print on white; the object is a French Duralex glass, which contains water to a level stipulated by the artist and which is located on a glass shelf, whose ideal height is 253 centimetres with matte grey-painted brackets screwed to the wall. The text is behind glass and is fixed to the wall with four bolts. Craig-Martin has stressed that the components should maintain a pristine appearance and in the event of deterioration, the brackets should be resprayed and the glass and shelf even replaced. The text contains a semiotic argument in the form of questions and answers, which explain that it is not a glass of water, but "a full-grown oak tree," created "without altering the accidents of the glass of water." The text defines accidents as "The colour, feel, weight, size...". The text includes the statement "It's not a symbol. I have changed the physical substance of the glass of water into that of an oak tree. I didn't change its