PAINTS and Varnishes are used by the engineer and builder for covering the surfaces of wood, iron, and other materials, in order to protect them from the action of the atmosphere, or to improve their appearance.

The preparation of surfaces and the different processes involved in painting and varnishing materials of different kinds have already been briefly described in Part II.

It will now be necessary only to give a few particulars regarding the paints and varnishes in common use on engineering and building works.

The paints used by the engineer and builder as a rule consist of a base1 (generally a metallic oxide) mixed with some liquid substance known as the vehicle; upon this, permanency of the paint depends.

In most cases a drier is added to cause the vehicle to dry more quickly, and a solvent is sometimes required to make it work more freely.

"When the final colour required differs from that of the base used, the desired tint is obtained by adding a stainer or colouring pigment.

It will be an advantage to glance at the properties of the substances used to effect the various objects above mentioned before describing the paints most commonly made from those substances.

The materials most commonly used for the purposes above mentioned are as follows :-

Bases

White lead, red lead, zinc white, oxide of iron.

Vehicles

Water, oils, spirits of turpentine.

Solvents

Spirits of turpentine.

1 Sometimes called a pigment, but here called the base in order to avoid confusion with the pigment added to give the colour; see p. 413.

Driers

Litharge, acetate of lead, sulphate of zinc, and binoxide of manganese, red lead, etc.

Colouring Pigments

Ochres, lampblack, umber, sienna, and many metallic salts, the principal of which are mentioned at pages 413 to 417.