During Ying Yangs talk about the restoration of Louise de Keroualle by Sir Godfrey Kneller we learnt a little bit about how colours for paints were made and used in the 17th century. One such colour was smalt – a ground blue potassium glass containing cobalt used between the 15th and 18th centuries. It was usually used for glazing ceramics, but was also very popular as an artist’s pigment because of its low cost and vibrant colour. It was a speciality of the Dutch and Flemish in the 17th century. Kneller was of German origin, so I suppose that he would have been aware of the properties of this pigment when he took up residence in London.

Over time the properties of the paint change depending upon various condtions such as light, dark, heat, cold and damp. In the case of smalt the oil in the pigment comes forward and the colour recedes backwards. The colour trhen changes – either to become lighter, darker or even almost disappear. Then it is known as a fugitive colour. This is exactly what happens with smalt – the colour is so vibrant when first applied but then almost completely vanishes. The blue of the silk cloak that Louise’s right hand is leaniing on has faded to a murky, insignificant pale blue. It is easy to see the brushstrokes on the canvas but there is little pigment left.

The cropped part of the painting also shows a young black girl on the left side. She must have been a later addition as she does not feature on the mezzotint that was made shortly after the original in 1684. We can see that the copy is reversed and Louise’s hand is resting on a piece of display furniture topped with a cushion and a crown. On the opposite side where now we just see some form of window and a king charles spaniel there is a classical column. It is so interesting to think about what prompted these changes and to wonder about the role of restoration – should works of art be brought back to the original? Should the smalt colour be reintroduced?