Table 1 Summary of the composition of the ground preparation, pigments, fillers, and extenders identified in the paint layers, as well as surface alterations and degradation processes detected in the three Van Gogh paintings analyzed in this study. A list of samples removed is also provided along with an indication of the micro-invasive techniques used to examine them. Non-invasive investigations by means of IR and UV photography, X-radiography, point XRF, and MA-XRF were performed on all three works

Roadway with Underpass (1887)

VG1) Cross section of ground and paint layers

SEM/EDS

Two-layer ground: bottom layer (10–20 μm) is mostly calcium sulfate, with traces of silicates, lead white, P, Fe, and Zn; upper layer (10–40 μm) is mostly lead white as a mixture of cerussite and hydrocerussite, with traces of Mg, Al, P, Ca, Fe, and Zn

Lead white, zinc white, vermilion, red lakes, iron-containing earths, chromium-containing pigments including chrome yellow and viridian, emerald green, cobalt blue, barium sulfate, calcium-containing compounds

Non-original, discolored varnish (oil, Pinaceae and Pistacia resins); biodeterioration (diacetoxyscirpenol); degradation layer composed of S-, Pb-, and K-containing compounds over the upper layer of ground

VG3) Cross section of ground and paint layers

SEM/EDS

VG4) Cross section of ground and paint layers

SEM/EDS

S7) Scraping of ground

FTIR, Raman

S8) Scraping of brownish-gray layer covering the surface

FTIR, Py-GC/MS

S9) Scraping of varnish

FTIR, Py-GC/MS

Landscape with Snow (1888)

S2) Cross section and scraping of canvas and ground

SEM/EDS, FTIR, Raman

Two-layer ground: bottom layer (100–120 μm) is a mixture of chalk and lead white, with traces of Al, Si, Mn, and Fe; upper layer (approximately 20 μm) is mostly lead white

Lead white, zinc-containing pigments, vermilion, eosin red and other red lakes observed by optical microscopy, iron-containing earths, umber, cadmium yellow, chromium-containing pigments including chrome yellow and viridian, emerald green, cobalt blue, cerulean blue, ultramarine blue, Prussian blue

Fading of eosin red and possibly of other red lakes

S3) Cross section of ground and paint from greenish-blue area of sky

SEM/EDS

S4) Cross section of ground and paint from lilac-blue area of sky

SEM/EDS

S5) Scraping of pink paint underneath purple strokes

HPLC-PDA

S6) Cross section and scraping of red-brownish paint

SEM/EDS, Raman

S7) Cross section and scraping of purple paint with pink underneath

SEM/EDS, HPLC-PDA

Mountains at Saint-Rémy (1889)

No samples were removed from this painting

–

Lead white

Lead white, zinc white, iron-containing earths, eosin red lake, chromium-containing pigments including chrome yellow and viridian, emerald green, cobalt blue, likely Prussian blue

Fading of eosin red