then did she lave her head with the mingled water and wine , and as she did so she sang a third song , a song of uttermost sleep , and the hair of tinuviel which was dark and finer than the most delicate threads of twilight began suddenly to grow very fast indeed , and after twelve hours had passed it nigh filled the little room , and then tinuviel was very pleased and she lay down to rest ; and when she awoke the room was full as with a black mist and she was deep hidden under it , and lo !