|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 MgSO4||
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|