That was because they were dyed with a chemical called alum, which was primarily found in Anatolia, in the Ottoman Empire. So to make the textiles the Ottomans craved, the Italians needed Ottoman alum, at least until 1460, when Giovanni di Castro, Pope Pius II's godson, discovered alum in Italy, in Tolfa. And he wrote to his godfather, the Pope, Today I bring you victory over the Turk. Every year they wring from the Christians more than 300,000 ducats for the alum, with which we dye wool various colors. But I have found seven mountains so rich in this material that they could supply seven worlds, if you will give orders to engage workmen, build furnaces, and smelt the ore, you will provide all Europe with alum, and the Turk will lose all his profits. Instead, they will accrue to you. So the Pope was like, heck yeah!