Answer:
He painted most of the background on location near Ewell in Surrey. He then had his model (Lizzy Siddal) pose in a bath of water heated from underneath by candles in his studio. At one point the candles ran low and poor Lizzy, fearful of saying anything to break the concentration of Millais, remained in the rapidly cooling water. This incident made her very sick and her father threatened legal action against Millais until he agreed to pay her doctor's bill.