One of the great aspirations of generations of painters has been to paint like the Old Masters, and in many cases that means like Rembrandt. At the time that he painted them, his late works were often criticised for their rough and sketchy facture, but they have since become greatly admired by the likes of Sir Joshua Reynolds, who spent years trying to rediscover ‘Rembrandt’s secret’.

Many, perhaps most, of the Masters have painted a scene from the Biblical story of Bathsheba, one of the more sordid but strongly visual of its histories.

King David lusted after Bathsheba, a gentlewoman of fine birth who was married to one of David’s generals. Having made her pregnant adulterously, David first tried to make it appear that the unborn child had been conceived in wedlock, then when that failed he put Bathsheba’s husband into danger in battle, so that he was killed, and David became able to marry her as a widow.

Other paintings portraying Bathsheba have generally centred on the lust and voyeurism of King David, secretly watching her naked while she bathed in the open.

Rembrandt’s first painting of Bathsheba at her Toilet in 1643 followed this pattern, only his model was past her best, and the distant voyeur king has disappeared into the gloom of old varnish, I presume to the left. But over the next dozen years, the artist came up with a very different treatment which addresses some of the issues raised by the Old Testament story.

In his second version, he opts for a very different scene. Bathsheba has received David’s letter which presumably lays bare his sinful intent. She is therefore pictured thinking over his desire for her, and for the ultimate fate of her husband.

By this time, Rembrandt’s personal circumstances had changed. His wife Saskia had died in 1642, and in the late years of that decade he began a relationship with his maid, the much younger Hendrickje Stoffels, which was getting her into trouble with her church. He was living way beyond his means, and by 1656 was on the verge of bankruptcy, which was further complicated by the conditions of a trust set up to support his son Titus. His self-portraits show the effects of age and these stresses only too clearly.

In spite of all these pressures on Rembrandt, his art just got better and better. When he came to paint his second version of the story of Bathsheba, he chose Hendrickje Stoffels as his model. She was pregnant by the middle of that year, but Rembrandt shows none of the physical signs of pregnancy in the painting.

Clutched in Bathsheba’s right hand is a letter, the title tells us from the king himself. Her eyebrows are raised in surprise, and she stares dreamily down at her attendant. We must presume that this letter is the king’s invitation to her to join with him in adultery. Rembrandt skilfully heightens the suspense in the lighting, and enhances the intimate detail with Bathsheba’s jewellery and ornamented hair. The crumpled sheets behind her make it clear that David’s invitation isn’t to a public engagement, but to a very private one.

The smooth skin of Bathsheba’s body, caught in the soft light, contrasts with the folds and crumples of the fabrics, the shift and robe, which are fashioned with visible, often quite coarse, brush-strokes.

Rembrandt’s late paintings came to create visual effects as much by surface textures, as by form or colour. One of Rembrandt’s secrets which so many have sought therefore lies in how he was able to exploit surface texture in this way – thus, in his paint. That is the ‘secret recipe’ which later self-appointed experts like Maroger and Redelius claimed to have discovered.

Systematic analyses of Rembrandt’s paint layers by White and others soundly rebutted the ‘secrets’ claimed. In the main, Rembrandt used linseed oil as his binder, occasionally using walnut oil as well, and just once poppy seed oil.

In some passages the oil had been thickened by heat treatment, but this was by no means widespread. Traces of pine resin found in some samples may have been introduced during retouching, and don’t appear to be a feature of Rembrandt’s impasto work; neither is there any evidence that he added wax to his oil paint to give it body (a favourite claim ever since the early visual examinations of Eastlake).

White’s research at the National Gallery in London was followed by the Rembrandt Research Project, which included analyses of samples from The Jewish Bride (c 1667) and other notable late works.

The width of this close-up view of fabric is about 30 cm (12 inches). There is a wide range of different types of mark, and degrees of organisation in different parts of the paint layer.

A similar-sized area from another fabric shows very different structure and texture.

That later work suggested that Rembrandt’s secret might have been the addition of small amounts of egg to the paint, but subsequent work has reversed that by suggesting that the analyses were more consistent with lead soap formation in the paint layer, not from the presence of egg proteins.

Others have suggested that Rubens and Rembrandt may have discovered how to make thixotropic oil paint, which is both easily brushable and retains brushmarks. As no one else appears to have made oil paint with such properties, that remains purely theoretical.

What few seem to have considered are the five hundred years of experience, of many painters and their workshops, in getting oil paints to just the right viscosity and handling, despite the effects of different pigments. If the illustrious predecessors of Rubens and Rembrandt were able to produce oil paints which handled right using (mostly) linseed oil and pigment, was there ever any need for dark secrets? Surely the reason that no one before Rembrandt exploited surface texture in the ways that he did, is because earlier painters wanted a flush, smooth surface, not because they were technically incapable.

For me, though, looking at Rembrandt’s late works, the greatest mystery is how he was able to work on the paint surface from a distance of less than a metre, producing visual effects which are only visible when viewed from several metres away. That is surely the product of great experience, vision, and true genius – Rembrandt’s real secret.