Mischtechnik or mixed technique[1] is a term spanning various methods of layering paint, including the usage of different substances.
As such, the old masters found ways of extending the natural advantages of its emulsion to create lean, siccative, smoothly transitional, semi-transparent layers of paint.
The visual effects created by working in the mixed technique essentially rely upon the phenomenon of light refracting through many subsequent layers of paint.
One common approach is to transpose the main compositional elements of a value study onto a panel using India ink, then slowly build up volume by alternating egg tempera with an overall glaze of oil paints mixed with resin, producing a jewel-like effect.
It is unforgiving of pentimenti, yet full of delightful surprises, since many unexpected colors can naturally arise during the ongoing glazing process.