Selected ranges in the U-band spectrum displaying the “curtain”. This is mostly produced by ground transitions from neutral and singly ionized metals and completely absorbing the continuum blue-ward of the Balmer jump. The top panel shows the whole wavelength range 3200–4100 Å; the middle and the bottom panels show zoomed in portions of the curtain. Black, blue, yellow, light-blue, red and dotted-gray are for epochs 1, 2, 3, 4, 5, and 6, respectively.