Mel Ramsden (b. 1944, UK)
Secret Painting, 1967-8

AGNSW attributes this piece to Art & Language although it also states that it is signed by Ramsden. I did not dig into reasons behind. They may remain secret to me as well.

A lot of interesting things are going here. Another take on the Black square. A question to what extent artist’s intention for the work can ever be known for sure. A question of how and by whom meaning of a work is created. A question of what and to what extent needs to be made accessible to the audience for an artistic experience to be had. A question of the difference between the content and the form. An epistemological condition of the artwork in general.

I am testing many of those aspects myself, so this is most relevant.