Table 2 Natural, processed and artwork samples classified by regions, prepared, analysed, and compared. The age refers to the geological timescale (G) for natural and processed samples, and the creation period (C) for artworks

France [4]

Champagne

Late Cretaceous (G)

Processed

CC

Meudon

Late Cretaceous (G)

Natural

ICr

Processed

IC

Paris, Ile-de-France

Early nineteenth century (C)

Easel painting, Hauts-de-Seine, France

FN

Germany [15, 37]

Sassnitz, Ruegen

Late Cretaceous(G)

Natural

RCr

Processed

RC

Lippstadt, Westphalia

fifteenth century (C)

“St.-Margaret” from the Master of Liesborn, National Gallery of London

NGL-Li

Belgium [38, 39, 41]

Mons

Late Cretaceous (G)

Natural

BCr

Processed

BC

Flemisch area, Brabant

Last quarter of sixteenth century (C)

Oil painting on wood panel, Seine-Maritime, France

SM

England [42, 43]

Cromer Beach, Norfolk

Late Cretaceous (G)

Natural

ECr

Italy

Bologna [44], [45]

Messinian-Tortonian (G)

Processed

IBC

Italy

Unknown

Sarti Chalk; Processed

SC

Vicenza [46], [47]

Cenozoic-Mesozoic

Processed

VWE