Probably by Rembrandt, 'Portrait of Margaretha de Geer, Wife of Jacob Trip', 1661

This is an excellent example of how tricky it is to be sure who painted a picture made more than 350 years ago. Until recently, people thought this portrait must be by Rembrandt. After all, on the left, a little below shoulder height, you can just make out the signature in his usual style, along with the date, 1661.

Another strong clue is that this is clearly Margaretha de Geer, the wife of the extremely wealthy arms dealer Jacob Trip – Rembrandt painted portraits of each of them in or around 1661. They are very large canvases and hang together in the National Gallery today. This painting is a smaller version of the portrait of Margaretha – the face is very similar, as are the clothes she is wearing. Surely, we might think, she liked the way Rembrandt depicted her first time around, and immediately commissioned him to make another portrait, either for herself or perhaps for one of her children or grandchildren. Lastly, the quality of painting is extremely high – this is a convincing likeness, rendered with great skill and worthy of an artist of Rembrandt’s stature.

However, in the late 1980s, technical analysis revealed unexpected differences between this and other paintings produced by Rembrandt. In particular, the materials used for the ground are unusual, though not unknown, for the seventeenth century, and certainly different from the kind Rembrandt usually used. The way that the canvas was mounted on the frame also differs from his normal practice. Neither of these inconsistencies are hard proof that Rembrandt or his workshop did not prepare the canvas. But, because they are unusual, they have also focused attention on some differences in style between the two portraits of Margaretha.

In this version, the paint has been applied with more fluidity and speed. Look, for example, how the brush has made swirls around her mouth and the sides of her nose, compared with the more precisely applied colour in the other portrait. And while Rembrandt has worked on the face of the larger portrait with enormous care, there are several places where the artist of this version has left the ground unpainted – the areas around her left temple and above her left eye are good examples. The folds and highlighted outlines of Margaretha’s ruff are also rendered slightly differently in each painting.

Again, such variations in technique do not prove that Rembrandt had no part in the painting. Maybe he was forced to work much faster on this portrait than on the other. Perhaps, having just done one, he felt more confident of capturing a likeness, so simply worked more swiftly. Perhaps he was simply experimenting with different techniques – he had used a more rapid, fluid technique in, for example, his portrait of Margaretha’s husband.

As for the signature, unfortunately we can’t rely on that either. Rembrandt’s name was often forged on unsigned paintings which have survived from when he was alive, and also on some made long after his death. However, in this case, the date is consistent with the other portrait, and it is unlikely that it would have been added without a signature.

We will probably never know for sure. But because the two paintings normally hang near each other in the same gallery, they provide a good opportunity to try to divine, and get closer to understanding, the hand of Rembrandt.