In whitening an old paper-lined ceiling that has gone a bad colour, clean off the ceiling and remove all loose paper; then apply a coat of size, which may be made by dissolving 6oz. of glue in 6pt. of water, and stirring in a handful of plaster-of-Paris. To make a good job, line the ceiling with lining paper and butt the joints; for a strong job, catch-lap the joints. The ceiling may then be whitened in the ordinary way. If the ceiling is a very large one, use Irish moss instead of size with the whiting, as the moss will keep the joints from setting.