Earth pigments

As the name implies, these stains are sprayed on and require Httie if any wiping. The solvent itself penetrates into the pore and allows the pigment and a small amount of binder to remain on the surface. These stains usually are composed of an oil-type vehicle and a combination of earth pigments reduced in a combination of aHphatic and aromatic hydrocarbons such as naphtha and toluene. The solvent system itself plays a big role in the appearance of the stain owing to the varying degrees to which solvents penetrate. Restrictions on the use of certain aromatic hydrocarbons have affected the manner in which these stains work. 

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. 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]...

Domenech A, Domenech-Carbo MT, Edwards HGM. (2007) Identification of earth pigments in severely damaged frescoes by applying multivariate chemometiic methods to solid state voltammetry. Electroanalysis 19 1890-1900. 

Earth pigment n. Class of pigments, which are usually mined directly from the earth, dried, generally Calcined and ground. Typical examples are red and yellow oxides of iron, yellow ochre, raw and burnt siermas, and raw and burnt umbers. Syn mineral pigments and natural pigments. 

Green earth Naturally occurring earth pigment, which is primarily an iron silicate. Used to make lime green. Syn terre verte. 

Vandyke brown van- dlk braun [fr. its use by the painter Vandyke] (ca. 1850) n. (1) A very dark, deep-brown natural earth pigment consisting essentially or organic matter obtained from peat or lignite found chiefly in parts of Germany its principal uses are in artists colors, stains and graining. (2) A synthetic pigment of similar color. 

Earth Pigments Those pigments that are obtained from the earth, including barytes, ocher, chalk and graphite. 

A term used by the seventeenth-century Spanish author Pacheco in his Arte de la Pintura, it is, according to Veliz (1986), the name of a dark reddish-brown pigment used in fresco, likely to be an earth pigment. 

Burnt sienna is the calcined, oxidised equivalent of the naturally occurring earth pigment (raw) sienna q.v.). The pigment, as Church (1901) writes, has a beautiful, warm reddish hue . Heaton (1928) adds that it is a very transparent pigment with excellent colour . 

Earth pigments group Iron oxides and hydroxides group Manganese oxides and hydroxides group Ochie Sienna Umber Wad Yellow ochre Bikiaris et al. (1999) Church (1901) 231 Harley (1982) 90 Heaton (1928) 118 Toch (1916) 71-72 Townsend (1996)... 

Pliny (1st cent AD/Rackham, 1952) XXXVxxvii, XXXV.xxx Earth pigments group... 

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