Hi Lily.

There is only ONE fresco technique which is BUON (in English translation True) Fresco. Pigments mixed with water must be applied to the wet (fresco) lime plaster before lime in the plaster "sets" - calcium carbonate is formed as a result of carbon dioxide from the air combining with the calcium hydrate in the wet plaster. Pigments are being imbedded in newly formed Calcium Carbonate crystals.

more on this pages:

http://www.truefresco.com/technique.html

http://www.truefresco.com/albuquerque.html

However there are two "extensions" to Buon fresco technique:

MEZZO Fresco and SECCO Fresco

MEZZO Fresco - the painting is done after plaster is "set" but still moist. In this case lime is mixed into the paint itself and forms a thin layer of colored crystals on the surface of the wall. The plaster has to still be moist - not cured completely for this painting layer to adhere. Mezzo Frescoes are not as durable as Buon Frescoes.
Mezzo Fresco technique was mostly used for decorative work (faux finish of a sort). Popular in Pompea.

SECCO Fresco - technically is not fresco at all, but an egg tempera. Pigments are mixed with eggs which(eggs) serve as a binding agent. It is used to correct minor defects and to make small adjustments to Buon frescoes. Also sky were often painted in secco due to the cost of a blue pigment and difficulty to hide the "cut-line" of the giornatas.
This secco technique has very limited durability and does flake of the wall in time, it is also can not be successfully restored - "Last Supper" by Leonardo was painted entirely in secco and it is now in very poor condition and it is practically unrestorable.

To learn fresco painting take our workshop - classes are awailable nationwide: Los Angeles, Denver CO, Luisvile KY.

for class schedule and prof. levels go to:
http://www.truefresco.com/workshop