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Sienna (from (イタリア語:terra di Siena), "Siena earth") is an earth pigment containing iron oxide and manganese oxide. In its natural state, it is yellow-brown and is called raw sienna. When heated, it becomes a reddish brown and is called burnt sienna.〔''Shorter Oxford English Dictionary'', 5th Edition (2002)〕 It takes its name from the city-state of Siena, where it was produced during the Renaissance.〔''Webster's New World Dictionary of the American Language,'' College Edition, (1964)〕 Along with ochre and umber, it was one of the first pigments to be used by humans, and is found in many cave paintings. Since the Renaissance, it has been one of the brown pigments most widely used by artists. The first recorded use of ''sienna'' as a colour name in English was in 1760.〔Maerz and Paul ''A Dictionary of Color'' New York:1930 McGraw-Hill Page 204; Color Sample of Sienna: Page 37 Plate 7 Color Sample E12〕 ==Sienna and the earth colours== Like the other earth colours, such as yellow ochre and umber, sienna is a clay containing iron oxide, called limonite, which in its natural state has a yellowish colour. In addition to iron oxide, natural or raw sienna also contains about five percent of manganese oxide, which makes it darker than ochre. When heated, the iron oxide is dehydrated and turns partially to haematite, which gives it a reddish-brown colour. Sienna is lighter in shade than raw umber, which is also clay with iron oxide. but which has a higher content of manganese (5 to 20 percent) which makes it greenish brown or dark brown. When heated, raw umber becomes burnt umber, a very dark brown.〔 File:Monteriggioni0001.jpg|The clay soil of Tuscany (here near Monteriggioni) is rich in limonite, or hydrated iron oxide, the main ingredient of sienna pigment. File:LimoniteUSGOV.jpg|Limonite, a clay containing iron oxide, which gives the color to sienna pigment. File:Hematite.jpg|Haematite. When limonite is roasted, it turns partially to haematite and becomes more reddish. File:Pigment sienna burnt iconofile.jpg|After being heated, the pigment has become the colour known as burnt sienna. 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「Sienna」の詳細全文を読む スポンサード リンク
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