Suddenly I'm an art dealer and my late wife has become an artist. I feel like one of those mediums who go into a trance and "write" a new symphony under the personal supervision of Mozart or finish The Mystery of Edwin Drood at the dictation of Charles Dickens.

There aren't too many upsides among the downsides of a brain tumour but it is a fact that without this cranial cancer Ruth's work would never have made it up on the gallery wall. The so-called "benign" growth that took 21 years to run its course did her one favour: it turned her into a painter. Of course, she will not see it herself on display but those formerly linked to her by genes or a joint mortgage will take pride for her in the wonderful swirls of paint she produced so casually.

She began to paint about a year before she died. This was purely as therapy. She had the chance of choosing a weekly course when she was attending the day centre at St Christopher's Hospice in south London. It could have been gardening but she chose painting.

She had earlier been forced to give up any artistic attempts after a couple of lessons from professional artist Anne Lynch, when it became apparent that her (dominant) right hand and arm were too affected for her to attempt anything representational.

Now, using the "wrong" hand, she did not have sufficient mental or physical control to do much more than vaguely striped designs. Yet under the tuition of the art staff, she produced vibrant artwork. Then Victoria Moore, our brilliant social worker, suggested that, on the six days a week when she wasn't on the course, Ruth carried on painting at home.

After that, the careworkers would wheel Ruth every morning to the kitchen table, where she would get stuck into the pots of paint. Here she dominated her designs and gave a very old-fashioned look to anyone making suggestions or, on one (and only one) occasion, making a mark on the paper.

She illustrated all our Christmas cards. Her largest paintings, which might take two days, were on squares of wallpaper. Whatever the size, her work consisted of amazing swirls and dabs of colour. As if in compensation for the closing down of her normal abilities, some unknown source of creativity was released.

Looking at the paintings, you might see landscapes at sunset or choppy waves or the flames of flickering forest fires. I don't think she was intending to trigger these images in our minds. Towards the end, she could not have known what waves and fireswere. One design was inspired by Monet's images of his water garden but a friend looking at it declares confidently that it is of a Scottish island with beach, boat and bystander.

She could not do anything that the rest of us could: walking, talking coherently, thinking cogently. But she could do something that none of the rest of us could achieve: arranging those colours in these vibrant patterns.

Were her paintings any good? In terms of art in general, I don't even know what I like (although, of course, I knew who I loved) and Ruth was outwardly dismissive about her own productions. A week before she died - as an in-patient at St Christopher's - she indicated that she wanted to handle the selection of works we kept in her room in the hospice: "That's beauty," she said, the last time she uttered a compete sentence.

Usually she affected to be amazed that we liked the paintings enough to stick them up on the kitchen wall. She would be even more amazed to learn that they will be up on a gallery wall for three months.

A friend working at the Institute of Psychiatry in Camberwell, on the south London medical site where Ruth was treated, suggested we offer some of her paintings for its gallery space. The exhibitions held there have some sort of medical element, such as autism or madness. Ruth Sale - In Living Colours has just opened and is curated by Anne Lynch. We are keeping the original artworks, since they were among the last things she touched, but are selling reproductions, with the profits going to St Christopher's.

A private view of the works raised several hundred pounds. Some of the kind remarks about the paintings came from people working in the building - this is just as well as they will be lumbered with Ruth's daubs every working day until the end of November. The social worker came up with yet another of her ideas: perhaps at the end of its three months at the IoP, the exhibition could be transfer to another site in Southwark. The exhibition may move, even though the artist couldn't.

A COLOURFUL IMPRESSION

‘Ruth Sale – In Living Colours’ is at the SGDP Centre, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, 9am to 5pm, Mondays to Fridays until December 1. Please phone the Institute of Psychiatry on +44 (0)20-7848 0873 in advance.