Two Sundays in every month I work as a volunteer at a small art gallery in North London. It is probably one of the most delightful jobs I've ever had - surrounded by sumptuous paintings and sculptures. Bathed in colour. It's like being dipped into an aesthetic, painterly spa. A blissful experience.

The visitors are fun, they're knowledgeable, curious, and many are artists themselves. And I learn which is a state of mind I can never get enough: about colour, the daring uses of a palette, the deliberation behind brush strokes, the motivations that fired the artist's sensibility.

You know that thinking is a promiscuous activity, you hop around, one thought leads to another then another, then one more, and so on.

I spent a very pleasant afternoon yesterday idly wondering what all the artworks do when the curator and staff have turned the alarms, locked the last door, and are receding footsteps across a crunchy gravel drive. Do the images in paintings squeeze out of the canvas, give themselves a shake and pop into three dimensions, and then reflect on the day ? Are there rhomboidal shapes leaning against walls popping a beer whilst talking football with a sturdy, heavy set farmer of the Dutch School? Are there gaily dressed flighty courtesans a la Hogarth flirting with Poussin's satyrs? Anyone hissing "bitch...she gets all the attention... and why...?" at the Mona Lisa?

Or are they sat around talking about us - the visitors and the staff ? "I had that bald guy again...straight up to the canvass...his breath...Jesus..." "...did you hear that crap about colour field theory....where do they get this from...?" "You can go years stuck on these walls before you hear anything that even resembles an original thought..." "...another canoodling couple...and they think they're the first...seen it all..." "Why do they stare so much...rude, man..." "see the students were back...and do they come over to see us ? No, straight to the Hoppers and the De Chirico's every time...and people wonder why I look so glum..."