when we paint something ,often we make a sketch first and then make a bigger painting from it. In this process the spontaneity we see in the smaller sketch is lost. the reason , I feel is that we try to add the details not found in the smaller sketch. We paint more 'carefully'. This carefulness results in loss of sontaneity.
To avoid this we should refrain ourselves from this tendency. Another thing is that when we paint in a bigger size we should use proportionally bigger brushes. The tools we use determine what we have to do.
What do you think ?
Here is the example. The lower one (7X10") is the sketch from which the upper one(11X15") was done.