Much too precise for what an artist might call eye-balling it

Much too precise for what an artist might call "eye-balling" it. This would mean either that a copy of the engraving, carefully squared up, exists, or that Van Gogh used some other mechanical means. Perhaps in a hospital in St Remy there might have been an epidiascope for lectures or medical diagrams. He might have immediately seen the possibilities of transferring the engraving to his canvas, and I'm sure he would not have hesitated to use this technique.

This in no way diminishes the deeply moving painting - it is more interesting than the engraving. To add colour to black and white would have pleased Van Gogh (there is a painting of his mother in the Norton Simon Museum in Pasadena done from a photograph, and Van Gogh mentions he wanted to add colour to this image). So, back to Ingres.I looked closer and closer and began to think that some mechanical device must have been used here. I remembered many years ago buying a camera lucida: I tried it for a day, found it too difficult to use, and forgot about it. So I asked Richard to nip down to our local art store and buy one - I knew they would have one I made a drawing of Richard using it.

It is a very simple device - quite small, really just a prism, but it enabled me to place the eyes, nose and mouth very accurately. I then drew from direct observation.It is merely a tool to place positions very precisely. You have still to be extremely observant and skilful with the pencil and only Ingres could make drawings like this. When I first suggested my theory to art historians they seemed horrified, as though this knowledge would diminish the work Why, I don't know. Who else made drawings as good as these? Ingres witnessed the birth of photography. His rival Delaroche made the statement, on seeing the daguerreotype, "From today painting is dead." He perhaps meant that the hand inside the camera had been replaced with chemicals.I think the history of photography and painting in the 19th century has yet to be explored.

People hide things - trade secrets as it were - but it is interesting to note that Degas, a great admirer of Ingres, was fascinated with photography. Cezanne did not care for Ingres and his work is very unphotographic. It seems to me that there is an interesting story here, and not just about the biographies of the sitters. Delaroche couldn't have foreseen that his remark about photography wasn't going to apply forever. Few people can see that, even today.The period of chemical photography is over - the camera is returning to the hand (where it started) with the aid of the computer All images will be affected by this The photograph has lost its veracity We are in a post-photographic age. Even in movies this is happening, in Jurassic Park and the new Star Wars What it means I do not know.