Memory can be a strange thing. I like to think that mine is rather good, although I've been accused of being a born story-teller, never allowing the facts to get in the way of an entertaining reinvention. Recently I've found evidence of memory having failed me in a way which has quite ruffled my confidence, with the emergence of disjunctions between the hard facts of a painting which I thought I'd studied carefully and my account of it written a short time later.

In 2003, I stood before Mategna's painting of Saint George in the Venice Accademia, rooted to the spot for half an hour by the painter's cool, ravishing vision. Later that day I wrote a detailed description of it in a notebook, to which I've subsequently referred on innumerable occasions. In the absence of a postcard reproduction, my description summoned the spirit of the painting for me as I toyed with the idea of making a contemporary version of it in homage.

Earlier this year I searched idly for an online image of the Mantegna Saint George. When I found one, it was apparent that something quite odd had occurred to my recollection of the painting after I'd left the gallery. The screen did not display the image that I had in my head. I had written that the saint stood on the body of the felled dragon, which  is not the case, and had been impressed by the unlikely delicacy with which the painter had balanced the lance in the saint's fingertips, rather like a violin bow at rest. Again, not so. Moreover, I had written that this slender, implausibly fragile weapon had pierced the beast clear through the skull. Wrong.

I still can't quite get to grips with the disjunction between my notes and the image of the painting on my laptop, but it's a relief that I got a couple of things right. I correctly remembered the wings were a vivid red, furled closely, almost shyly, against the saint's back, and that in his elegant carapace of parade-ground armour, he was as slender-waisted as a hornet.

Flight of Swallows Over the Field of Gold is what might be described as an imaginative evocation of the Mantegna-painting-that-never-was. The saint finally stands on his vanquished foe, and his lance, now quite as slender as I misremembered, pinions the hellish creature's head to the earth. However, the landscape in which the drama unfurls is the Ystwyth Valley, with the hundred and fifty year-old holly tree in our garden as a backdrop and the birds which reared their noisy young in the space above my studio ceiling serving as models for the 'Swallows'.