If the plaster is new, any caustic alkilinity should be corrected. This can be done by applying a coat of linoleic acid or boiled linseed oil. Linseed oil contains naturally linoleic acid in sufficient quantity. If linoleic acid is used, it must be applied warm. A wash of water containing carbonic acid gas will kill the caustic lime by converting it into lime carbonate which is neutral. A coating of liquid silicate of soda may also be used. This forms, with the lime, an insoluble silicate of lime. The above suggestions apply, whether the painting is to be done with oil or water colors.

White lead and raw linseed oil, with litharge dryer, mixed rather thin, is a good wall priming.

When perfectly dry, a second coat somewhat heavier in body can be applied. The second coat may contain 1-4 turpentine. If a third coat is required for very durable work, and a gloss is desired, use 2 parts oil to 1 part turpentine. If a flat finish is desired, use equal parts of oil and turpentine.

A priming of caseine mixed with cement makes a good surface on which to paint.