Skip to main content

Table 3 Key findings resulting from the analysis of W&N AOC cadmium yellow (CY) and French ultramarine (FU) tube paint samples

From: The influence of light and relative humidity on the formation of epsomite in cadmium yellow and French ultramarine modern oil paints

Paint samples Ageing conditions LM SEM–EDX ATR-FTIR XPS XRD
CY 75% RH, elevated light Diamond-shaped and hexagonal-shaped crystals observed on the paint surface. Samples aged at 75% RH/elevated light conditions presented a superficial surface layer positioned underneath/surrounding seeded crystals. Both seeded crystals and the superficial layer were rich in Mg, S and O
The superficial surface layer appeared similar to the layer observed after ageing at 75% RH/near-dark conditions, which lacked seeded crystals.
The emergence of SO42− absorption bands at 1087 cm−1 after ageing, is consistent with the formation of a sulphate salt. Samples aged at 75% RH/elevated light contained a higher abundance of SO42− species relative to the sample aged at 50% RH/ambient light. The emergence of additional diffraction patterns after ageing supports the crystals to be MgSO4·6H2O
75% RH, near-dark Colourless superficial dendritic layer visible across the paint sample surface, but no large surface crystals. N/A N/A
FU 75% RH, elevated light Rod-shaped and hexagonal crystals observed on the paint samples after ageing at 75% RH under both elevated light and near-dark conditions, but crystals were more abundant for elevated light aged samples;
“cross-shaped” radial crystals only seen for samples on acrylic-primed canvas.
A superficial surface layer rich in Mg, S and O (indicating magnesium sulphate) underneath/surrounding seeded radial crystals rich in Na, S, and O (indicating sodium sulphate) was observed for samples on acrylic primed canvas, aged at 75% RH/elevated light.
The surface layer appeared similar to that observed in cadmium yellow paints after ageing at 75% RH.
The emergence of SO42− absorption bands at 1100 cm−1 after ageing at 75% RH indicates the formation of sulphate salts. This may arise from the sodium enriched seeded crystals theorised to be Na2SO4, or the Mg enriched surface layer likely to be MgSO The emergence of SO42− species is evidenced by changes in O 1s and S 2p environments after ageing at 75% RH/ elevated light relative to ageing at 50% RH/ ambient light
A stronger Na 1s signal also suggests an increase in Na species at the sample surface after ageing at 75% RH/ elevated light
See Section 3 in Additional file 1
75% RH, near-dark Small hexagonal surface crystals were observed, however these were generally less abundant relative to the samples aged at 75% RH/elevated light. N/A N/A