I just discovered this beautiful book by Walt Disney artist Albert Hurter, he worked on Snow White amongst other brilliant creations. The book has been kindly shared by the excellent Michael Sporn Animation Studio, here is the link to
part1,
part 2,
part 3 part 4,
part 5,
part 6 . Also worth checking out is the book by
Ferdinand Horwath, another great Disney artist from the 1930's. There's enough inspiration here to keep you occupied for months.....