JL Twenty years ago, we talked mostly about your contribution to the exhibition, Light from the Dark Room. It was Source (1995). The work had presented very severe technical difficulties – the photographing of a thread. What could be more minimal? But at last you pulled off a wonderful piece. Composed in five large panels with the symmetry of an altarpiece, darkness prevailed at the centre – a fathomless nothingness mitigated by a tiniest blue shift towards the vertical edges. The flanking panels take up the shift which becomes a pulse running across the whole piece. A white line of absolute stillness, bisects vertically the panels next to the centre. It's the thread. At last, in the outer panels – like the end of the orchestral introduction of Haydn's Creation and the words ‘and there was light’, when a huge sound bursts forth – a great vibration of the thread (or string) is caught. And out of that motion, induced directly or indirectly, was created, in the darkness, light – the photographer's medium. It was an epic work. What became of it”

DW Yes, Source was quite a challenge to produce. I think I used just about every light in the studio to make it, and many, many reshoots were required. The work was acquired by the National Galleries of Scotland and had more outings. It was included in the Narcissus (2001) exhibition of self-portraiture at the Portrait Gallery, curated by Julie Lawson.

JL A self-portrait?

DW Yes. Among other things, the work alludes to the ‘birth of consciousness’. It's ‘Self’ with a capital letter, not me in the mirror.

JL I see. The self-effacing nature of the universal proposition allows the work to be part of the viewer's mental life rather than some sort of inner secret of the artist. I guess that's the nub of its memorableness.