Late in the 1700s, American farmers began painting their barns with homemade wood preservatives to protect them from the weather. In the northern states where winters are particularly harsh, the preservative found to offer the best protection was one made from lime, skim milk, and red iron oxide. When this mixture dried, it gave the barn a durable, plasticlike finish. Because of the iron oxide, it also gave the barn a bright red color. The use of this preservative became so widespread that by the early 1800s red had become the traditional color for barns.