Spanish hematite

Figure 3.18 illustrates typical square-wave voltammograms of earth pigments attached to graphite electrodes in contact with O.IOM HCl. Voltammetric curves can, in principle, be grouped into five morphological types whose holotypes are depicted in Fig. 3.18 [139, 174], These holotypes correspond to (a) Spanish hematite, (b) French yellow ochre, (c) sienna raw, (d) Italian toast umber, and (e) greenish natural umber [139, 174].

Fig. 12.30 Relationship between the fraction of oxidic Fe dissolved by dithionite/citrate/bicarbonate in 30 min and the proportion of Fe in hematite in hematitic/goethitic clay fractions of some Spanish soils (Barron Torrent, 1987, with permission).

Fig. 3.19 Plot of I(II)/I IV) vs. for earth pigments differentiating hematite-based (solid rhombs), goethite-based clays (solid squares), siennas and Spanish ochre (rhombs), French ochres (squares), and umbers (triangles). From square-wave voltammograms of pigment-modified PIGEs immersed into 0.10 M HCl. Potential scan initiated at -fO.65 V in the negative direction potential step increment 4 mV square wave amplitude 25 mV frequency 5 Hz [139]...

Hematite is found in large quantities in the vicinity of Malaga in Spain (Spanish red) and near the Persian Gulf (Persian red). The Spanish reds have a brown undertone. Their water-soluble salt content is very low and their Fe203 content often exceeds 90 %. The Persian reds have a pure hue, but their water-soluble salt content is disadvantageous for some applications. Other natural hematite deposits are of only local importance. A special variety occurs in the form of platelets and is extracted in large quantities in Karnten (Austria). This micaceous iron oxide, is mainly used in corrosion protection coatings. 

Persian Gulf red oxide is derived from Ormuz Island. The hematite deposits contain about 72% Fe203 and are the highest-chroma naturally occurring red oxide. Spanish red is derived from hematite deposits near Malaga, Spain, and contain about 90% Fe20> It is less saturated than Persian red and contains carbonates, limiting its use in acidic media. 

Iron oxides and hydroxides group Hematite Iron(lll) oxide, hematite type Kadinite Burnt vitriol Cerussa Colcothar Copperas Red lead Spanish brown Tyrian purple Venetian red... 

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