A fresco is a wall-painting made using the buon fresco technique of applying pigment to freshly mixed, wet plaster. The process results in durable, permanent images. Another technique, known as fresco secco, is a method of applying pigment to plaster than has already dried. This method results in more fragile images that can flake off over time. Fresco painting is usually done in areas with warm, dry weather—ideal conditions for the buon fresco process. Italian cities such as Florence and Siena are well known for their frescos.