Probable Palette of Pigments Based on XRF Analysis

For the Hogarth portraits, XRF analysis suggests that the artist's palette consisted of just a few paints and likely included the following pigments:

Blue - Prussian blue (Fe4[Fe(CN)6]3 )

Red - vermilion (HgS), an organic red, and possibly red lead (Pb2O4)

Yellow - yellow ochre (Fe2·H20, clay, etc.)

Brown - mixture iron oxides (Fe2O3) and bone black [Ca10(PO4)6(OH)2]

White - lead white [2PbCO3 Pb(OH)2]

Black - bone black [C + Ca3(PO4)2]

Ground Preparation Layer - chalk (CaCO3) tinted with an iron oxide (Fe2O3)

XRF analysis also indicates the presence of potassium in every area of the painting tested. Since no strong correlation exists between the presence of potassium and any of the specific paints tested, its presence requires an alternate explanation. One such explanation is that the formulation of all the paints incorporated a potash-based soap. Potash is derived from wood ash and was commonly used during Hogarth's time to create soap. Potash contains potassium carbonate, potassium hydroxide, and potassium oxide.

Image: Detail of Hogarth Painting the Comic Muse, c. 1758-64, engraving on cream wove paper, plate size 40.4 x 35.4 cm, Gift of Richard Ward Greene, 1913.95.2

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