Application of Varnish - In using varnish great care should be taken to have everything quite clean, the cans should be kept corked, the brushes free from oil or dirt, and the work protected from dust or smoke.
Varnish should be uniformly applied, in very thin coats, sparingly at the angles.
Good varnish should dry so quickly as to be free from stickiness in one or two days. Its drying will be greatly facilitated by the influence of light; but all draughts of cold air and damp must be avoided.
No second or subsequent coat of varnish should be applied till the last is permanently hard, otherwise the drying of the under coats will be stopped.
The time required for this depends not only upon the kind of varnish but also upon the state of the atmosphere.
Under ordinary circumstances spirit varnishes require from two to three hours between every coat; turpentine varnishes require six or eight hours; and oil varnishes still longer, sometimes as much as twenty-four hours.
Oil varnishes are easier to apply than spirit varnishes, in consequence of their not drying so quickly.
Varnish applied to painted work is likely to crack if the oil in the paint is not good; also, if there is much oil of any kind, the varnish hardens more quickly than the paint, and forms a rigid skin over it, which cracks when the paint contracts.
The more oil a varnish contains the less likely it is to crack.
All varnishes improve by being kept in a dry place.