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Investigating surface treatments and coatings, their history, application and detection on selected pigments: Lead White, Zinc White and Titanium White
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The present work looks at pigment surface treatments and is divided in two parts. Part I explores
the relationships between pigment manufacturers, raw materials suppliers, and the artist’s oil paint
manufacturer, and describes surface treatments and coatings. This is followed by a summary of the
history and characterization of surface treatments and introduces the role of pigments in the
formation of certain paint defects in relation to these surface treatments. Finally, it presents a
tentative identification of the surface treatments of the white pigments selected for study. The
research in Part I involved collecting information through research into the patent and technical
literature in conjunction with interviewing a global manufacturer and supplier of raw
materials/pigments and an artist’s oil paint manufacturer. This exploration revealed that pigment
surface treatments can be very complex consisting of either an inorganic or organic component or
both, applied in very small amounts (up to 10% wt of the pigment). This work revealed that surface
treatments may find their origins very early on, as in the 14th century Montpellier Manuscript, and that
treatments re-emerge in response to industrial uses and needs not specifically linked to artist’s oil
paint manufacturers. Materials such as waxes and stearates, known additives for oil paints, but also
alkyds, developed as organic binders, were found to have been used as surface treatments for
pigments.
Part II focuses on the detection and identification of surface treatments on the selected pigments,
Lead White, Zinc White and Titanium White, and describes the multi-analytical approach used to
investigate their surface treatments with electron microscope techniques (SEM-EDX, FEG-SEM and
(S)TEM-EDX) and hyphenated mass spectrometry techniques (EGA-MS, Py-GC//MS and Py-THMGC/
MS, and DTMS). This study highlights the importance of gathering information on the pigment’s
provenance and material characterization and reflects on the implications of terminology and
commercial secrecy for surface treatment detection and identification. Regarding the detection and
identification of inorganic treatments, both FEG-SEM and (S)TEM-EDX proved to be effective for this
purpose. These techniques also provided evidence which shed light on the method of manufacture of
the pigments. Although the analysis of the organic fraction present in the pigment samples proved to
be challenging, pyrolysis methods did enable the identification of anticipated materials (as was the
case of the polyols in Titanium White pigments) as well as the discovery of unexpected compounds
such as anti-oxidants.
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Surface treatment Titanium White Lead White Zinc White Pigment