Intro to buon (true) fresco:
Buon fresco is a painting technique that requires applying pigments, usually suspended in water, onto a thin layer of freshly made lime plaster. Because of the chemical makeup of the plaster, paint binders such as egg, oil, or glue are not used. As the plaster reacts with the air the pigment particles are locked into the plaster's surface in a protective crystalline mesh known as the lime crust. Essentially, the artist is painting "into" rather then "onto" a wall.
Buon fresco contrasts with the secco technique as the later consists of applying pigment with a binder such as oil, egg, or glue onto an already dried plaster wall. In essence, secco fresco is a paint film that is stuck to -but not an integral part of- the wall.
Because the buon fresco technique requires a fresh plaster surface, the demands and working conditions are extremely unique. Frescoists must plaster only what they can paint in a single day and trim away the unfinished areas at the end of the painting session. This single day's work is referred to as a "giornata", or a group of days' work as "giornate". Any mistakes must be corrected when the wall is dry in the "secco", or for extreme mistakes, the section must be chipped away, re-plastered then painted again.
Additional requirements include using lime safe (alkaline resistant) and light-fast (light resistant) pigments for outdoor mural painting. Traditionally, pigments made from oxides (rusts) were relied upon for fresco as they were known to be chemically stable when used with lime plaster.
Fresco has been viewed historically as a mural technique that oftentimes blurs the lines between painting and architecture, image and wall. The construction method used in the Van Meter fresco included five layers of plaster, starting with a course scratch coat and ending with a fine white painting surface, known as the "intonaco". While frescoeists throughout history have always used the same basic materials (lime, aggregate, water, pigment) their construction methods varied in the same way that other construction methods vary from culture to culture. The quantity of layers, thicknesses, exact make up of the plaster, and general working processes are things that are situational and regional.