Thinking back to my last post, and Hester Thrale’s comment about Sir Joshua Reynolds’s falling-out with his sister Frances, it is worth saying that in the late 1770s he did not have much to worry about in terms of rivalry from other artists. A while ago I was lucky enough to see the two large group portraits of the Dilettanti Club that Reynolds painted at this date; they are extraordinary, and I can’t find a reproduction to do them justice.

(c) Society of Dilettanti.

This one of the pair stood out particularly, because it showed how much great painting is all about light. Making a group portrait animated and plausible is an achievement in itself, but the Dilettanti Club portraits go far beyond that. Reynolds plays some conventional illusionistic tricks with heavy shadows; when the painting was originally hung at one end of the Great Subscription Room at Brooks’s it would have seemed that the shadow lower right was cast by the room’s actual architecture; and the shadow under the folio of Sir William Hamilton’s vase collection on the table projects the book and the imaginary world of the sitters out into  the real space of the viewer. But it is the mass of flickering lights throughout the painting that brings it to life; they break up the surface, give shape to the wineglasses that are so beautifully, believably painted and keep the eye moving from face to face, reminding us that in life nothing is still even for an instant.

It is one of those paintings that make you crane forward trying to find the trick that shows how the painter does it, and frustrates you, because close to it breaks down into a mass of rapidly worked strokes that only coalesce at a distance. Rembrandt was a master of this. I remember seeing this 1628 self portrait when it was on tour from the Rijksmuseum, and being amazed that when you put your face right up to it, the illusion disappeared. The dark areas in shadow at the top of Rembrandt’s face are just the plain dark ground of the canvas, with his shadowed eyes blocked in; the flesh tones is only painted in the cheek, neck and nose where it is highlighted, and there the impasto is so thick that it becomes disorienting, almost abstract. But that was not how Rembrandt meant his work to be viewed. As Sir Godfrey Kneller remembered, Rembrandt would tell people who put their faces right up to his brushwork: ‘My pictures were not made for smelling of.’

(c) Rijksmuseum, Amsterdam

The suggestion that objects are defined by light rather than their own solidity reaches its height in the Nineteenth Century; Walter Sickert is one of my favourite artists for the way he luxuriates in oil paint, creating pictures you just want to run your fingers over. The way that the dresser and mirror in Mornington Crescent Nude 1907 appear to dissolve in the sunlight from the window is a triumph of light and texture. A painter creates the picture as much from the dots you join in your head as the strokes they put down on the canvas.

(c) Estate of Walter Sickert/ DACS. Gallery of New South Australia, Adelaide