White lead

Common name for lead hydroxide carbonate (II), Pb ₃ CO ₃ (OH) _2. Formerly known as basic lead carbonate, white lead, or Chinese earth. A heavy powder with a hexagonal crystal system. It is the oldest white pigment, and was the only pigment with great hiding power until zinc oxide, titanium white, and zinc sulfide came into use. However, because it is toxic and soluble in organic acids, its use was restricted and its production volume dropped dramatically.

Generally, the German method, in which a mixture of carbon dioxide, air, acetic acid and water vapor at 50 to 70 degrees Celsius is pumped into a room containing many hanging thin lead plates, producing lead hydroxide carbonate on the surface, is said to have the greatest concealing power.

It has high light resistance and weather resistance, and is stable up to 150℃. It is attacked by sulfur dioxide and turns black with hydrogen sulfide. When used as a paint, it creates a coating with good adhesion and elasticity, so it is used as an undercoat for wood and as a top coat for exteriors.

[Jun Otsuka]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

炭酸水酸化鉛（Ⅱ）Pb₃CO₃(OH)₂の慣用名。古くは塩基性炭酸鉛ともよび、白鉛、唐土(とうど)ともいう。六方晶系の重い粉末。もっとも古い白色顔料で、亜鉛華、チタン白、硫化亜鉛が使用されるまでは、唯一の、隠蔽力(いんぺいりょく)の大きい顔料として用いられてきたが、有毒かつ有機酸に溶けるため、使用上の制限を受け、生産量は激減した。

　一般には、薄鉛板を数多くつり下げた室に、50～70℃の二酸化炭素、空気、酢酸および水蒸気の混合ガスを送り、表面に炭酸水酸化鉛を生成させるドイツ法によるものが、隠蔽力が大きいとされている。

　耐光性、耐候性ともに大で、150℃まで安定。二酸化硫黄(いおう)に侵され、硫化水素により黒変する。塗料として用いると、付着性、弾性のよい塗膜をつくるため、木部の下塗り用、外部上塗り用に使用される。

［大塚　淳］

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