after listening to the great Mike Azevedo I decided to follow his advice and do a sketch after doing a study. It is meant to stay in the memory better and I think he is right.
So here is a 1h study and a 1 h painting from memory.
If you don't know Mike Azevedo: https://www.youtube.com/watch?v=0a_Si9LejaI
older work: http://mikeazevedo.blogspot.de/
newer work: https://www.artstation.com/artist/mikeazevedo
Follow him, study him, he is a beast.