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All colours of Greek black-red vase painting are produced by the different concentrations of iron in the clay, and the different degrees to which that iron is oxidised during firing. Iron has the special feature of forming oxides of various colours, including grey Iron(II) oxide (FeO), red Iron(III) oxide (Fe 2 O 3), and deep black magnetite ...
Ochre (/ ˈ oʊ k ər / OH-kər; from Ancient Greek ὤχρα (ṓkhra), from ὠχρός (ōkhrós) 'pale'), iron ochre, or ocher in American English, is a natural clay earth pigment, a mixture of ferric oxide and varying amounts of clay and sand. [2] It ranges in colour from yellow to deep orange or brown.
If in light ochre the content of the main dye, iron oxide hydrate, is quite low and ranges from 12 to 25%, then in golden ochre its amount can reach 70-75%. As a result, light ochre has a yellow color of a cooler tone and weaker color saturation and is considered a paint that is not bright and not intense.
Clay earth pigments (naturally formed iron oxides) Raw umber (PBr7): a natural clay pigment consisting of iron oxide, manganese oxide and aluminum oxide: Fe 2 O 3 + MnO 2 + n H 2 O + SiO 2 + Al 2 O 3. When calcined (heated) it is referred to as burnt umber and has more intense colors. Raw sienna (PBr7): a naturally occurring yellow-brown ...
Red ochre – natural minerals containing silica and clay some of which is composed of iron oxide and hematite (anhydrous iron(III)-oxide) Yellow ochre – natural minerals that contain silica and clay, and attributing to its color, goethite (iron oxyhydroxide) Lime white – chalk (calcium carbonate and calcite)
Goethite is an iron oxyhydroxide containing ferric iron. It is the main component of rust and bog iron ore. Goethite's hardness ranges from 5.0 to 5.5 on the Mohs Scale, and its specific gravity varies from 3.3 to 4.3. The mineral forms prismatic needle-like crystals ("needle ironstone" [3]) but is more typically massive. [2]
Among the primary types of earth pigments include the reddish-brown ochres, siennas, and umbers, which contain various amounts of iron oxides and manganese oxides. [ 1 ] [ 2 ] Other earth pigments include the green earth pigments or terres vertes , blue earth pigments such as vivianite -based "blue ochre", white earth pigments such as chalk ...
Iron oxides feature as ferrous or ferric or both. They adopt octahedral or tetrahedral coordination geometry. Only a few oxides are significant at the earth's surface, particularly wüstite, magnetite, and hematite. Oxides of Fe II. FeO: iron(II) oxide, wüstite; Mixed oxides of Fe II and Fe III. Fe 3 O 4: Iron(II,III) oxide, magnetite; Fe 4 O ...
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