Examining the idea of layers in the style of Leonardo Da Vinci

The main focus on experimenting and examining layers in the style of Leonardo Da Vinci was on his piece 'Head of a girl'; this piece was chosen because it shows layers in different ways.

Different pencils are layered which created different tones, which then adds more shape and detail to the piece.

I focused mainly on the face to convey how Leonardo Da Vinci uses layers, however incorporated his use of rough sketch marks which also add line and shape to the piece.

Leonardo Da Vinci uses the combination of the layered pencil which creates tone and texture and the mark making: it creates an unfinished look, which applies emphasise on the bolder and more tonal areas of the piece.  

The layers of marks that Leonardo Da Vinci sometimes uses in his sketches are rough and create texture.
I attempted to convey the rough sketches from a section of his piece 'Study of hands'.
Layers are formed when the marks overlap, the line then creates tone and adds shape to the piece.
Also, in some cases, Leonardo Da Vinci annotates on his sketches, this creates layers to the piece due to adding more layers and meaning to the piece.