Chrome ochre

Chromium, 122 ppm of the earth s crustal rocks, is comparable in abundance with vanadium (136 ppm) and chlorine (126 ppm), but molybdenum and tungsten (both 1.2 ppm) are much rarer (cf. Ho 1.4 ppm, Tb 1.2 ppm), and the concentration in their ores is low. The only ore of chromium of any commercial importance is chromite, FeCr204, which is produced principally in southern Africa (where 96% of the known reserves are located), the former Soviet Union and the Philippines. Other less plentiful sources are crocoite, PbCr04, and chrome ochre, Cr203, while the gemstones emerald and ruby owe their colours to traces of chromium (pp. 107, 242). 

Occurrence. The ore of Cr of higher commercial importance is chromite (FeCr204). Other minerals are crocoite PbCr04 and chrome ochre Cr203. About 2% Cr in emerald Be3Al2Si6018 is the source of its green colour. Chromium is comparable in abundance in the earth s crustal rocks with V and Cl. 

Chromic Oxide, Chromium Sesquioxide, CrgOg, which occurs naturally in chrome ochre (see p. 8), exists in both amorphous and crystalline forms. The amorphous form may be obtained by calcination of a mixture of three parts of potassium chromate with two parts of sal-ammoniac by heating potassium dichromate with sulphur . ... 

Silicates of chromium have not been prepared. Numerous siliceous minerals contain chromium sesquioxide, generally in combination with the oxides of aluminium and iron, e.g. chrome ochre and wolchonskoite (see p. 8). 

Anadonis Green, Chrome Ochre, Green Cinna-har, Green Rouge, Leaf Green, Oil Green,... 

Prussian blue and a yellow chromate (qq.v.). The mineral form is eskolaite (q.v.) Salter (1869) states that [oxide of chromium] is found native in an impure state as chrome ochre, but is always artificially prepared for artistic use . 

Chromate and bichromate of lead—known respectively as lemon and orange chrome, or as chrome yellow and chrome red—yellow ochre, gamboge, and other pigments, furnish a yellow hue. 

The principal red and yellow pigments are Lead chromate chrome yellow, orange and red), zinc chromate zinc or buttercup yellow), barium chromate lemon yellow or yellow ultramarine) various products based on jerric oxide, hydrated (yellow) or anhydrous (red), both natural yellow and red ochres) and artificial Mars yellow, English red, etc.) red oxide oj lead minium or red lead) mercuric sulphide cinnabar, vermilion) antimony oxysulphide antimony cinnabar) cadmium sulphide cadmium yellow) basic lead antimonate Naples yellow). 

Yellow ochres are earths composed essentially of clay coloured by hydrated ferric oxide they may contain siliceous sand, calcium carbonate, small proportions of manganese oxides, and sometimes basic ferric sulphate and calcium and barium sulphates. Chalk, gypsum and heavy spar may be added fraudulently and the colour may be " improved by artificial organic dyes, vegetable colours or chrome yellow. 

Yellow ochre may be " improved, besides by artificial organic dyes, also by vegetable colours or by chrome yellow. These are detected by treatment with sodium hydroxide from the alkaline solution of vegetable colours, the corresponding lakes are precipitated by addition of aluminium sulphate the same alkaline solution, acidified with acetic acid, gives a yellow precipitate in presence of chrome yellow. 

Titanium dioxide, zinc oxide, white lead, lithopone, antimony trioxide Carbon black, mineral black, black iron oxide Synthetic iron oxide, red lead oxide, cadmium red Chrome yellow, strontium yellow, zinc yellow, nickel titanate yellow, zinc chromate, earthen iron oxide (ochre)... 

Coal Ochre Ultramarine Berlin blue Brunswick green Chrome green Chrome yellow Green cinnabar Prussian blue Heaton (1928) 380 Linke Adam (1913) 70 Mierzinski (1881) 120 Rose (1916) 220, 349 Salter(1869) 79... 

Hematite Lead chromate(VI) oxide Ochre Chrome orange-. Chrome red-, Red ochre... 

Baryte Gamboge Brunswick green Chrome yellow, Dutch pink, Prussian blue, Viridian-, Yellow ochre... 

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