Table 2 Results of the multi-analytical characterisation performed on the samples

Artworks

A2

Cd, S (Zn)

NA

Poorly crystalline CdS/Cd_1−xZn_xS

NA

NA

Oil (2916, 2847,1714 cm⁻¹)

Carboxylates (1537 cm⁻¹)

Sulfates (1096, 606 cm⁻¹)

Oxalates (1615, 1319 cm⁻¹)

Drying oil, likely linseed oil (P/S = 1.87), relatively dried (A/P = 1.21, O/S = 0.40)

CdS/Cd_1−xZn_xS (238, 305, 346 cm⁻¹)

Oil (869 cm⁻¹)

3CdSO₄·8H₂O (476, 983, 1006 cm^–1)

Unassigned: 411 cm⁻¹

Homogeneous µs emission along the paint stratigraphy, broad and weak, peaked at 700 nm (DTS CdS/Cd_1−xZn_xS)

A7

Cd, S (Zn)

Cd, S (Zn)

NA

Poorly crystalline CdS/Cd_1−xZn_xS (bulk)

3CdSO₄·8H₂O (surface)

Sulfide (bulk)

Sulfates (surface)

Oil (2925, 2850, 1706 cm⁻¹)

Carboxylates (1560 cm⁻¹)

Sulfates (1087 cm⁻¹)

Drying oil, likely linseed oil (P/S = 1.78) as stand oil (typical markers of pre-polymerisation treatments), relatively dried (A/P = 1.17, O/S = 0.15)

CdS/Cd_1−xZn_xS (218, 238, 305, 346 and 633 cm⁻¹)

Oil (869 cm⁻¹)

3CdSO₄·8H₂O (476, 983 and 1006 cm^–1)

Unassigned: 411 cm⁻¹

Spatially heterogeneous emission, with the paint surface displaying a broad and intense µs emission peaked at 695 nm (DTS CdS/Cd_1−xZn_xS), very weak emission from the bulk

A9

Cd, S (Al, Si)

Cd, S

NA

Poorly crystalline CdS/Cd_1−xZn_xS (bulk)

3CdSO₄·8H₂O (surface)

Sulfide (bulk)

Sulfates (surface)

No FTIR spectra due to strong resin background

Drying oil, likely safflower oil (P/S = 2.20), very dried (A/P = 1.45, O/S = 0.02)

CdS/Cd_1−xZn_xS (238, 305, 633 cm⁻¹)

3CdSO₄·8H₂O (476, 983 and 1006 cm^–1)

Unassigned: 411 cm⁻¹

Spatially heterogeneous emission, with the paint surface displaying a broad and intense µs emission peaked at 690 nm (DTS CdS/Cd_1−xZn_xS), very weak emission from the bulk

Oil paint tubes

A3

Cd, S (Mg, Al)

NA

Crystalline hexagonal CdS

NA

NA

Oil (2917, 2850, 1705 cm⁻¹)

Carboxylates (1563 cm⁻¹)

Mg-carbonate (1455, 1415, 873, 822 cm⁻¹)

Mg-sulfate (1080, 983 cm⁻¹)

Drying oil, likely linseed oil (P/S = 1.35), not very well dried; traces of beeswax and alkyd-based resin; high amount of unsaturated oleic and linoleic acids

No Raman bands detectable due to strong fluorescence

Homogeneous emission in the paint layer, with a sharp and strong ns peak at 517 nm (NBE CdS) and a broad µs peak above 800 nm (DTS CdS)

A5

Cd, S (Zn)

NA

Poorly crystalline CdS/Cd_1−xZn_xS

Poorly crystalline CdS/Cd_1−xZn_xS

Mainly sulfide, low quantities of sulfates

Oil (2924, 2853, 1738 cm⁻¹)

Carboxylates (1550 cm⁻¹)

Sulfates (1100, 610 cm⁻¹)

Drying oil, likely safflower/sunflower oil (P/S = 2.89), not very dried; traces of a Pinaceae resin (i.e., Colophony); high amount of unsaturated oleic and linoleic acids

CdS/Cd_1−xZn_xS (218, 238, 305, 346 and 633 cm⁻¹)

Oil (869, 1063, 1080, 1304, 1441, 1657, 1740, 2853, and 2909 cm⁻¹)

3CdSO₄·8H₂O (983 and 1006 cm^–1)

Unassigned: 411 cm⁻¹

Homogeneous emission with a weak ns sharp peak at 485 nm (NBE Cd_1−xZn_xS) and a broad µs emission peaked above 750 nm (DTS Cd_1−xZn_xS)

A6

Cd, S (Mg, Al)

NA

Crystalline hexagonal CdS

NA

NA

Oil (2920, 2850, 1701 cm⁻¹)

Mg-carbonate (3393, 1456, 1407, 826 cm⁻¹)

Mg-sulfate (1073,983, cm⁻¹)

Oxalates (1606, 1320 cm⁻¹)

Drying oil, likely linseed oil (P/S = 1), very well dried; metal soaps

No Raman bands detectable due to strong fluorescence

Homogeneous emission, sharp and strong ns peak at 515 nm (NBE CdS), broad µs emission peak above 800 nm (DTS CdS)

Artist palettes

A1

Cd, S (Zn)

NA

Poorly crystalline CdS/Cd_1−xZn_xS

NA

NA

Oil (2916, 2847, 1710 cm⁻¹)

Carboxylates (1537 cm⁻¹)

Sulfates (1082, 606 cm⁻¹)

Oxalates (1621,1319, 822 cm⁻¹)

Drying oil, likely linseed oil (P/S = 1.75), dried; traces of a Pinaceae resin (i.e., Colophony)

No Raman bands detectable due to strong fluorescence

Spatially heterogeneous emission, with the paint surface displaying a broad and intense µs emission peaked at 655 nm (DTS CdS/Cd_1−xZn_xS), weak emission from the bulk

A4

Cd, S (Zn)

Cd, S (Zn)

Poorly crystalline CdS/Cd_1−xZn_xS

Poorly crystalline CdS/Cd_1−xZn_xS

Sulfide (bulk)

Sulfates (concentrated in Zn rich region detected in the µXRF mapping)

Oil (2917, 2849, 1733 cm⁻¹)

Carboxylates (1540 cm⁻¹)

Sulfates (1100, 606 cm⁻¹)

Drying oil, likely linseed oil (P/S = 1.30), dried; traces of a Pinaceae resin (i.e., Colophony)

CdS/Cd_1−xZn_xS (238, 305, 346, and 633 cm⁻¹)

Oil (869, 1063, and 1080 cm⁻¹)

3CdSO₄·8H₂O (476, 983 and 1006 cm⁻¹)

Unassigned: 411 cm⁻¹

Homogeneous µs emission at 700 nm (DTS CdS/Cd_1−xZn_xS)

A12

Cd, S (Zn,Cl)

Cd,S (Zn)

NA

Poorly crystalline CdS/Cd_1−xZn_xS (bulk)

3CdSO₄·8H₂O (surface)

Sulfide (bulk)

Sulfates (surface)

Oil (2923, 2850, 1710 cm⁻¹)

Carboxylates (1540 cm⁻¹)

Sulfates (1097, 1043 cm⁻¹)

Oxalates (1612, 1317,827 cm⁻¹)

Drying oil, likely linseed oil (P/S = 1.45), dried; traces of a Pinaceae resin (i.e., Colophony)

No Raman bands detectable due to strong fluorescence

Spatially heterogeneous emission, with the paint surface displaying a broad and intense µs emission peaked at 650 nm (DTS CdS/Cd_1−xZn_xS), weak emission from the bulk