There is a really fascinating exhibition currently on display at the National Gallery in London:Painters' Paintings: from Freud to Van Dyck. The seed for this show was apparently the donation to the National Gallery of Lucien Freud's Italian Woman by way of the Acceptance-in-Lieu programme after Freud's death. Its arrival prompted the Gallery to investigate how many artworks in its possession had belonged to artists down the ages.  The result of this inventory is this wonderful, interesting exhibition.

Freud, Matisse, Degas, Lord Leighton, George Frederic Watts, Sir Thomas Lawrence, Sir Joshua Reynolds and Anthony van Dyck were all assiduous art collectors. Their reasons for seeking to own other artists' works resonate with every one of us artists around the world, I suspect. The impulse to own other people's art is very strong, for a variety of reasons, but to me, one of the predominant ones is that willy nilly, one has to live withthe art each of us creates, and ultimately that is somewhat "cannibalistic"; we need other people's works to sustain us. I know I love the art I own that friends have created - they form a precious group with which quietly to commune.

That sustenance and presence meets a number of diverse needs, according to each artist. Some artists collect art, particularly important works if they can afford it, for social prestige - the luster rubs off on them, as it were. But there are many other passions driving these collections: admiration for an artist, affection and friendship too.

Another aspect is a feeling of identifying with an artist in his or her way of painting and seeing the world; this often can imply too a desire to learn from and to be able to emulate the other artist's work and approach to making art.  Joshua Reynolds, for instance, used many of his paintings in his collection as teaching tools for his students. Others, like Matisse or Degas, closely studied other artists' work and were inspired by them to try new approaches to their own painting. In essence, artists often pay homage to other artists by wishing to own and live with their work.

The delicious availability of art that you love and own is a wonderful privilege too. You don't have to go off to a gallery or museum in order to commune with a drawing or painting - it is right there in your own home.  Degas, who had a huge collection as he could afford to collect Old Masters and his contemporaries from the word go, housed them very carefully on one floor of his three-floor abode in Paris and thus could go and study them at any time of day or night. Thus stimulation and inspiration from your collection come at any moment, even when the play of light is different on a piece, or whatever chance occurrence sparks something in the artist's eye.

Understanding how another artist achieves something is often a process of slow observation and thought - so much easier when you have a sample of that artist's work on your walls. There are often elements, too, of rivalry or a desire to emulate and do better, in the collections artists make of other art. Nothing is straightforward ever in human emotions, even over beautiful works of art!

Actually assembling a collection of other artists' works can be a long-term occupation. Gifts and exchanges between artists are frequent methods of building up a collection, especially when money is scarce. even Degas traded a lot of his work for pieces he really, really wanted. If the work is expensive or scarce, then auctions or agents helping to find the gems are often routes chosen. Sir Joshua Reynolds wanted a Raphael so badly that he just told his agent to get it, at any price!  Seeing it, one can understand why!

The aspect of "la chasse" also comes into this desire to possess - the hunt is always a galvaniser! And the trophy is cause for much jubilation and celebration when the artist succeeds in getting the artwork that is so desired.

Longer term, as Lucien Freud's desire that the National Gallery should own Italian Woman showed, there is always the concern about where this collection will end up. In our world today, ensuring that art remains in good hands after one has died is a complex undertaking.  Ideally the artist's family will also enjoy such work, but nothing is guaranteed, and there is always the tax man lurking too!!

Nonetheless, seeing what art an artist collects can give us wonderful insights into the artist and his or her approach to life. An understanding of that artist's mind helps us appreciate their work. As exhibition curator, Anne Robbins, wrote in the catalogue, "Painters' paintings form ephemeral groups of artworks, chosen - thus created - with artistic skill, sensitivity and inventiveness on the part of the painter who selected them. They represent the most secret kind of self-portrait: objects that do not bear the mark of the artist's own hand, yet convey the presence of their owner with the most intriguing material truth."