Cross sections of paint from the sea
Detail of the sea, showing the blue paint that was protected by the frame
Examination of the painting showed that the edges of the sea are blue, where the paint has been protected by the frame, and the main area of the sea, not protected by the frame is brown.
Samples of paint were made into cross sections and dispersions. These were examined under magnifications of up to 400 times with reflected and polarising light microscopy.
The cross section below was taken from an area of the sea protected underneath the frame rebate at the very edge of the painting. There are two distinct blue layers again here, but no evidence of any brown layer on the top. The clear line between the two layers shows that the top layer was probably applied over the first blue layer after it had dried. If the top paint layer was applied over wet paint it is unlikely there would be such a clear line separating them.
Cross section of a paint flake from the sea under the rebate, full width of image 0.625mm. Showing a top blue paint layer protected by the frame, the first blue layer underneath and the thick white ground layer under both
The image below is the same cross section examined in ultra violet light. Both blue layers fluoresce the same way, indicating that the same blue was probably used for both layers.
Cross section of a paint flake from the sea under the rebate in UV light, full width of image 1.25mm
The cross section below is taken from the main area of the sea which appears brown. Above the thick white ground, there are two distinct blue layers. The top one has an orange/brown tone to it which seems to be seeping into the blue layer. This sample is taken from the sea where the blue has discoloured to a brown colour.
Cross section of a paint flake from the area of the sea with a discoloured layer, full width of image 0.625mm. Showing the top discoloured blue layer visible in the sea, the first blue layer underneath and the thick white ground layer under both
The image below is the same cross section examined in ultra violet light. This shows the discoloured upper layer as a very dark layer. This is very different from the protected area of sea seen in the first cross section.
Cross section of a paint flake from the area of the sea with a discoloured layer in UV light, full width of image 0.625mm
This sample was also examined in the SEM (scanning electron microscope). A lot of lead was found in the uppermost layer, plus a small amount of iron and potassium, but it was not possible to identify the blue pigment used or why it had changed colour.