Over the centuries, several variants of dried fish have evolved. The "stockfish" (fresh dried, not salted) category is often mistaken for the "clipfish", or salted cod, category where the fish is salted before drying. After 2–3 weeks in salt the fish has salt-matured, and is transformed from wet salted fish to "clipfish" through a drying process. The salted fish was earlier dried on rocks (clips) on the foreshore. The production method of clipfish was developed by the Portuguese who first mined salt near the brackish water of Aveiro, and brought it to Newfoundland where cod () was available in massive quantities. Salting was not economically feasible until the 17th century, when cheap salt from southern Europe became available to the maritime nations of northern Europe.