[snip] To alchemists, lead was the lowliest of metals - in a sense, it was where all metals started. In talk of base metals, which alchemy tried to turn to silver and gold, there was none so base as lead. The alchemists believed that lead slowly matured into other metals in the ground. But alchemy also offered lead a chance to shake off its grey and graceless image. It does not take much to draw splendid colours out of lead. The ancient technologists blanched the dull metal by placing lead strips in pots with vinegar, and shutting them away in a shed full of animal dung. The vinegar fumes and gas from fermenting dung conspired to corrode lead into lead white. Heat this gently, and it turns yellow: a form of lead oxide known as litharge or, in the Middle Ages, massicot. Heat it some more, and it goes bright red, as you form a different kind of oxide. Both of these substances were used by artists - red lead was, for a long time, their finest red, used for painting many a bright robe in the Middle Ages. It was the signature colour of Saint Jerome.
To the alchemists, those colour changes weren’t just a way to make pigments. They signified some more profound alteration taking place in the metal, bringing it close to the colour of gold. It’s no wonder, then, that their experiments often began with lead. They came no closer to making real gold, but they started to explore the processes of chemical transformation.
Lead, however, seems habituated to revealing its true and dirty colours. Exposed to air, it may go on taking up oxygen until it turns black. Red lead has become chocolate brown on paintings throughout the world, from Japan to India to Switzerland. In urban galleries there is another danger, as the sulphurous fumes of pollution react with red lead to from black lead sulphide. There seems to be no getting away from it: lead has a glum and melancholy heart. [/snip]
Very good explanation that even this dummy could understand. And so beautifully written. Thanks.