From: Faded shine…. The degradation of brass powder in two nineteenth century paintings
Sample | FTIR diamond window | ATR–FTIR–FPA | GC–MS | LM | XRF | SEM–EDX | SRXTM | Overall interpretation |
---|---|---|---|---|---|---|---|---|
Metallic flakes | n/a | No signal | n/a | C01 and C02 yellow metal leaf fragment 1–4 μm thickness embedded in the varnish layer | Cu Zn | C01 Cu 84 Zn 16 Cl | C03 (same location as C2) Flat thin high X-ray absorbing particles carrying from 1 to 4 μm thick and up to 80 μm long. Bent and folded | Coarsely ground brass metal leaf applied over the paint |
Green agglomerates | 2918, 2850, 1585, 1467, 1420 cm−1 copper carboxylates 2918, 2850, 1540 cm−1 zinc carboxylates 1718 cm−1 free fatty acids | C01 2926, 1741, 1583, 1543, 1518, 1457, 1417 cm−1 copper and zinc and carboxylates C02 region one 2922, 2854, 1735 1585, 1540, 1525, 1455, 1418 copper, zinc and lead carboxylates in heterogeneous distribution | Methyl palmitate (P), methyl stearate(S) (P/S = 3), small amount of methyl oleate, methyl laureate, methyl myristate, dimethyl azelate and dimethyl suberate | C01 and C02 homogeneous dark green non-fluorescent mass. Wide range of thicknesses | Cu Zn | C01 Cu 83 Zn 17 | C03 (same location as C2) Large homogeneous low absorbing/scattering material. Shape closely related to the outline of the metal particles | Reaction between fatty acids with copper and zinc from the metallic pigment. Distribution of zinc and copper soaps is on locations heterogeneous. With higher zinc soap concentration on the upper areas of the soap agglomerates |
Paint build-up | n/a | FTIR–FPA C01 Red layer: 2925, 2850, 1738, 1168 sh cm−1 Oil 1520 cm−1 lead carboxylate 3522, 1398, 1044 cm−1 basic lead white 1100 cm−1 aluminium phosphate Pink layer: 2925, 2850, 1735, 1165 cm−1 Oil 1520 cm−1 lead carboxylate 3522, 1398, 1044 cm−1 basic lead white. 1151, 1078, 1019, 934 cm−1 starch C02 Grey layer: 2925, 2850, 1735, 1165 cm−1 Oil 1520 cm−1 lead carboxylate 3522, 1398, 1044 cm−1 basic lead white | n/a | C01 Red layer: red and white pigmented layer with few black particles Pink layer: White and red pigmented layer C02 Grey layer: Black, red and blue pigment particles sparingly distributed in a white pigmented layer | Same location as C01 Pb; Fe Sn Same location as C02 Pb; Fe Sn Sb | C01 Red layer: Pb containing white pigment particles Al, P containing red particles Pink layer: Pb Hg, S containing particles C02 Grey layer: Pb | C03 (same location as C2) Two layers. Top layer higher absorbing/scattering than the lower | Oil paint. C01 Red layer: red pigment on aluminium phosphate substrate. Lead white. Lead soaps Pink Layer: vermillion lead white C02 Grey layer: lead white, unidentified black, blue and red pigment particles |
Varnish | 2954, 2870, 1712, 1457, 1385 cm−1 natural resin possibly dammar 2934, 2859 sh, 1733 sh, 1415, 1245, 1102 cm−1 oil component | C01 2930, 2854, 1715 1456, 1391 cm−1 natural resin. 2933 sh, 2850 sh, 1732 sh, 1418, 1165, 1106 cm−1 lipid contribution C02 no clear signal | n/a | C01 Clear layer: 10 microns thick, embedding the metal particles and soap aggregates. Fluorescent under ultraviolet illumination C02 Clear layer: approx. 12 μm thick. Fluorescent under ultraviolet illumination | n/a | n/a | C03 too low X-ray absorption at the energy used and not distinguishable from the resin used to fix the sample on the holder. n/a | Natural resin varnish. Presence of lipids |