Author:Postrel, Virginia

RELIGIOUSLY TRAUMATIC AND militarily ominous, the fall of Constantinople in 1453 also created a crisis for the European textile industry. The problem, in a word, was alum.

To securely attach to fibers, most dyes need chemical help: a mineral salt known as a mordant, from the Latin word mordere, meaning to bite. Allowed to saturate the material before dyeing, the mordant bonds with the fibers and provides a bridge to bond with and fix the dye.

Alum, a potassium or aluminum sulfate, is the most important mordant. It "is no less necessary to dyers of wool and woolen-cloth than bread is to humankind," wrote Vannoccio Biringuccio in his 1540 book De la Pirotechnia. By the Middle Ages, alum mining, production, and trade were big businesses--the first international chemical industry. The typical alum operation mined alunite, a mineral found in volcanic areas, then heated the rocks in a kiln and repeatedly poured water over them until they formed a paste. The paste was then boiled and decanted to get rid of insoluble compounds, resulting in a saturated solution that crystallized into purified alum.

IN 1453, MOST of

Europe's alum came from rich mines in Anatolia--mines that the Turks suddenly held.

"The West could not get along without alum and, in order to get it, was thus forced to finance indirectly the Turkish campaigns," writes economic historian Raymond de Roover. To make matters worse, the Turks kept raising prices.

But just as the price of alum reached unprecedented levels, a seeming miracle occurred. A well-connected Paduan named Giovanni de Castro was walking through the volcanic Tolfa Mountains, west of Rome, when he spotted white minerals with the salty taste of alunite. Maybe it was an accidental discovery. Maybe he was deliberately prospecting. Either way, de Castro hit pay dirt.

"I announce to you a victory over the Turk," he triumphantly informed his godfather, Pope Pius II. "He draws yearly from the Christians above three hundred thousand gold pieces for the alum with which we dye our wool....I have, however, found seven hills so stocked with alum as to be nigh sufficient for seven worlds. From them you may supply all Europe....This mineral will give you the sinews of war, which is money, the while it takes them from the Turk."

The alum proved to be of good quality, and the location was ideal, with a nearby port and abundant wood for kilns and caldrons. Best of all, Tolfa was not just in Christian territory but in the pope's own...

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