Apparatus is disclosed for re-applying dye to a dye donor element of a dye transfer thermal printer. A reservoir contains a supply of dye that is thermally transferred from the reservoir to the dye donor element by diffusion of dye into the dye donor element. The reservoir has a diffusion controlled permeation membrane through which dye is delivered to the dye donor element, while inhibiting diffusion of a binder, whereby the dye diffuses between the reservoir and the dye donor element but the binder does not.