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Ochre ( ; from Greek: ὠχρός, ''ōkhrós'', (pale yellow, pale), also spelled ocher, see spelling differences) is a natural earth pigment containing hydrated iron oxide, which ranges in color from yellow to deep orange or brown. It is also the name of the colors produced by this pigment, especially a light brownish-yellow.〔''Shorter Oxford English Dictionary'' (2002), Oxford University Press.〕〔''The Random House College Dictionary'', Revised Edition, (1980). "Any of a class of natural earths, mixtures of hydrated oxides of iron and various earthy materials, ranging in color from pale yellow to orange and red, and used as pigments. A color ranging from pale yellow to reddish-yellow."〕 A variant of ochre containing a large amount of hematite, or dehydrated iron oxide, has a reddish tint known as "red ochre". ==Ochre and the earth pigments== Ochre is a family of earth pigments, which includes yellow ochre, red ochre, purple ochre, sienna, and umber. The major ingredient of all the ochres is iron(III) oxide-hydroxide, known as limonite, which gives them a yellow color. * Yellow ochre, FeO(OH)·nH2O, is a hydrated iron hydroxide (limonite) also called gold ochre * Red ochre, Fe2O3, takes its reddish color from the mineral hematite, which is an anhydrous iron oxide. * Purple ochre, is identical to red ochre chemically but of a different hue caused by different light diffraction properties associated with a greater average particle size. * Brown ochre, also FeO(OH), (goethite), is a partly hydrated iron oxide. *Sienna contains both limonite and a small amount of manganese oxide (less than five percent), which makes it darker than ochre. *Umber pigments contain a larger proportion of manganese (five to twenty percent) which make them a dark brown.〔 p. 30〕 When natural sienna and umber pigments are heated, they are dehydrated and some of the limonite is transformed into hematite, giving them more reddish colors, called burnt sienna and burnt umber. Ochres are non-toxic, and can be used to make an oil paint that dries quickly and covers surfaces thoroughly. Modern ochre pigments often are made using synthetic iron oxide. Pigments which use natural ochre pigments indicate it with the name PY-43 (Pigment yellow 43) on the label, following the Colour Index International system. File:LimoniteUSGOV.jpg|Limonite, a mineraloid containing iron hydroxide, is the main ingredient of all the ochre pigments. File:Hematite.jpg|Hematite is a more reddish variety of iron oxide, and is the main ingredient of red ochre. When limonite is roasted, it turns partially to the more reddish hematite and becomes red ochre or burnt sienna. File:Goethite-190288.jpg|Goethite, named for the German poet Goethe, is the main ingredient of brown ochre. This sample comes from the Leadville District in Colorado. File:Sentier des ocres 1.JPG|The clay hills of Roussillon, Vaucluse, in Provence have been an important source of ochre pigment since the 18th century. File:Roussillon sentier des ocres2.JPG|Yellow and red ochre along the Path of Ochres in Roussillon. File:Tonneau d'ocre rouge.JPG|A keg of ochre pigment at the ochre mines in Roussillon. File:Mina de Hematita terrosa.JPG|Red ochre underground mining. Province of Jaén, Spain. Drei verschiedene Ockertöne.JPG|three different ochre- pigments 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ochre」の詳細全文を読む スポンサード リンク
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