Usa "lose vitality" in una frase

1. Nevertheless, if this particular look of softness and fleshiness is desired, either the painting must be so thin or the tones so fused together that no brush strokes show, or a dry flat brush must afterwards be drawn lightly across when the painting is done, to destroy the downward brush strokes and substitute others going across, great care being taken to drag only from light to dark, and to wipe the brush carefully after each touch; and also never to go over the same place twice, or the paint will lose vitality