Margarito d’Arezzo: Orpiment

One of the oldest paintings in the National Gallery’s collection is 'The Virgin and Child Enthroned' by Margarito d’Arezzo, dated to about 1263–4.  It was purchased by the Gallery in 1857. 

The painting shows the Christ Child and his mother, the Virgin Mary, in a mandorla (an almond-shaped enclosure) surrounded by scenes of the nativity and from the lives of saints, all set against a gilded (gold leaf) background. 

During a recent conservation treatment, overpaint was removed from the wide red border of the inner edge of the frame to reveal an original red border with a foliate (leaflike) decoration.

This decoration was painted in a strongly-coloured yellow.

Orpiment is a yellow arsenic-containing pigment. It has a long history of use and has been identified in early European panel paintings, manuscript illumination and polychrome sculpture. It continued to be used by later artists, particularly in 16th-century Venetian paintings.  

Orpiment can degrade over time, decomposing to the white substance, arsenic trioxide.​​ However, in the foliate design, it has not degraded because it was protected by various layers above it, including a yellow glaze and the red overpaint.  

To identify where orpiment had been used in other areas of the painting, analysis using a non-destructive technique (scanning X-ray fluorescence) was performed. This technique can map where a specific chemical element is present. 

Here, arsenic-containing areas in this detail are shown in white on the map on the right. 

Since both orpiment and its alteration product contain arsenic, we can use this technical image to identify where orpiment was used, even if the pigment has degraded and no longer appears yellow in colour.