Following Henry VIII of England of England and his infamous "Great Debasement" program that began 1526, the Spanish King Philip III tried to cement his Spanish legacy through changes in coinage strategy. Previously, Spanish Kings (at least from 1471) issued a largely copper fractional coinage called blancas, with a nominal money-of-account value of 0.5 maravedí, but with a very small amount of silver to convince the public that it was indeed precious-metal "money". The blanca issued in 1471 had a silver fineness of 10 grains or 3.47% (weighing 1.107g). In 1497, that fineness was reduced to 7 grains (2.43% fine); in 1552, to 5.5 grains (1.909% fine); in 1566, to 4 grains (1.39% fine). By the start of the 17th century, inflation took hold of Spain as the gap between nominal and silver-based prices dramatically shifted. The purely copper coinage had done its damage to Spain. The difference between the silver- and vellon-based price indexes in Spain showed that the purely copper coinage other European countries used made up a much smaller proportion of the total coined money supply (something the Spanish Kings had overlooked and Malestroit was able to pinpoint).
Question: How many fewer grains did the blanca have in 1566 than it had in 1471?
Answer: 6