To gold-line mounts for pictures, prepare a solution of strong gum arabic, and add a small quantity of moist sugar; strain through muslin. Placing a ruler where the line is required, with a quill make a full line of gum. In a few minutes the gum will become "tacky," and gold leaf, cut in very narrow strips, may be applied with a tip, dabbed down and skewed in in the usual way. This process will give a clean, durable line. Gold lines made by applying gold paint turn black in a very short time.