Portrait of two brothers ("making of" and details included)

So I have been asked to do portraits of two boys and decided to paint it in more layers combining egg tempera and oil, like Van Eyck, Albrecht Durer, Hans Holbein, Otto Dix and others did. In each phase I have tried to be exact as possible. Up until these two portraits I have been painting a little less rational, but now I am trying to get myself used to this new but old technique of painting. 

First I used egg tempera to get the drawing done as exact as possible in black and white, with umber background (it really dries fast and gets done in one day). Next, I set the local tones of the hair, skin and clothes with oil and covered the background in a coat of Prussian blue to get a cold feel of the white I want to use as a background at the end. After it dried I used egg tempera again to put out the highlights and bring the texture of skin, hair and clothes back (egg tempera is really good for textures and drawing parts). After that comes the "irrational" part of painting in oil where I fix stuff and try to get the character of the model right.

 Egg tempera and Oil on board
20x30cm
2012.

Egg tempera and Oil on board
20x30cm
2012.