What does technique mean?
Lots of people conceive it as Photoshop, others think of it as do-it-yourself painting handbooks and stuff.
Let’s consider a 13th century fresco’s process of creation.

Firstly comes the Sbruffatura, to level the work surface.
Then the Arriccio, that is to say the mortar.
The Sinopia is next, the preparatory charcoal drawing.
The Intonaco (or lime plaster), whose composition is clay, water and marble dust, is finely coated over the sinopia.
Lastly, the colour is fixed on the wet, fresh plaster thanks to the carbonatation of the lime – the tonachino’s water evaporates and fixes the colour.

N.B.: Giotto revolutionized the organization of work, introducing shifts of the factory kind. The tonachino was therefore applied only on the surface’s portion which would be painted on the same working day – eight-hour shift, even at that time.

Right, let’s go back to Photoshop now.