Rembrandt's Self-Portrait At The Age of Thirty-Four is to be one of the superstars of the blocksplintering show Botticelli to Van Gogh: Masterpieces from the National Gallery, London, opening at the NGA on November 13.

As well as it being a criminal thing to do, touching the portrait, even getting too close to it, will activate loud sirens and alarm bells and will see the NGA's trained treasures-protecting leopard, Jackson, automatically unleashed to pounce on you, drag you away and tear you apart.

But I have got ahead of myself and of my theme. Putting Jackson back in his cage for the moment I muse that I have always had the vague sense (but till now have kept it to myself lest I be thought bonkers) that paintings, especially oil paintings, are in a sense alive, that they surely have a kind of a pulse.

Now an informative piece in The New York Times, Sophie Haigney's 'The Scream' Is Fading. New Research Reveals Why, shows that some of my poetic whimsies about paintings have a kind of basis in curatorial science.

On to Ms Haigney in a moment but first I leap to clarify that when I talk of paintings being living things I don't mean "alive" in the sense that, at night when there is no one to see them the figures in paintings come out to play (actually I believe that they do, but that's a subject for another time).*

Rather I mean that many paintings' surfaces and appearances have a hard-to-define, quasi flesh-and-blood quality suggestive of a gallery-goer's own mortality.

Faces in portraits, especially, half-seem to be made of skin. One fancies that if one reached out to caress a painted portrait's face, especially if it is an oil-painted face, it would feel very like touching the cheek of a living loved one.

Your columnist, a wisening, pock-marked 74, is especially skin-conscious these days because as one ages, having hitherto taken the skin for granted, one is increasingly having meaningful interfaces with dermatologists and coming to a late understanding of skin's moods and complexities.

And in her piece Ms Haigney, interviewing gun forensic conservators, discusses how some paintings, just like us, change their looks over time as time takes its tolls of complexions. There is "degradation" she explains.

The title of her piece refers to the fact that a 1910 version of Edvard Munch's world-renowned The Scream held in Oslo is fading with time. The skin on the famous contorted face is now more pale than it was when Munch daubed it.

Haigney reports that "Jennifer Mass, the president of the Scientific Analysis of Fine Art lab whose team is on The Scream research, explained the science recently in her lab. She pointed to a photograph of what looked like a set of stalagmites: It was the surface of The Scream seen under a microscope. 'This is really, really not what you want to be seeing,' she said. Nanocrystals are growing on the painting, held by Oslo's Munch Museum - stark evidence of the degradation near the central figure's mouth, in the sky and in the water."

"[And]" Haigney relates, "The Van Gogh Museum in Amsterdam and the Metropolitan Museum in New York have mounted exhibitions in recent years highlighting his [van Gogh's paintings'] disappearing hues."

"The colours of the late 19th century and early 20th century are fading especially rapidly," Haigney grieves, "because of changes that took place in paintmaking."

"Paints had been made by hand-grinding minerals extracted from the ground or using dyes made from plants and insects. The industrial revolution brought about the production of synthetic pigments like cadmium or chrome yellows, which artists would mix with oil and fillers. Artists began experimenting with these synthetic pigments, which were sometimes haphazardly prepared and untested for the purposes of longevity but were exceptionally bright - enabling the brilliant palettes of Post-Impressionism."

Does this mean, your columnist wonders, that the sunflowers of the van Gogh Sunflowers coming here for the Botticelli To Van Gogh extravaganza are no longer as radiantly, sunnily, sunflowery as they were when Vincent picked them, put them in a vase and daubed them in 1888? Yes, poignantly, it probably does.

"Interestingly," Haigney continues, van Gogh, among other artists, was aware of the pitfalls of the new pigments [being used in his times]. 'I've just checked - all the colours that Impressionism has made fashionable are unstable,' van Gogh wrote to his brother Theo, in 1888, 'all the more reason boldly to use them too raw, time will only soften them too much.' In a later letter, he wrote 'The paintings fade like flowers.' "

Isn't it very, very poignant (helping to explain the strange power of painted art) to know that oil paintings, just like us (and especially our complexions) are always in the process of fading like flowers? Don't try to embrace them (for Jackson will rip you apart) but the great works coming here for Botticelli and van Gogh are our perishable brothers and sisters.

*For example how is it that when one is an early morning visitor to David Hockney's swimming pool masterpiece A Diver (1978) in the National Gallery of Australia there is always water on the floor and a smell of chlorine?