Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/388

380 management. As copal swells while dissolving, so its solutions and varnishes contract, and consequently crack, in drying, and thence linseed oil is essential to prevent its cracking. The mixture of copal varnish and linseed oil is best effected by the medium of oil of turpentine, and for this purpose heat is sometimes requisite.

Iron-work, Varnish for. Dissolve in about 2 pounds of tar oil, $1/2$ pound of asphaltum and a like quantity of pounded resin, mix hot in an iron kettle, care being taken to prevent any contact with the flames. When cold the varnish is ready for use. This varnish is for outdoor work and iron-work.

Common work, Varnish for. Place 3 pounds of powdered resin in a tin can, and add $2 1/2$ pints of spirits of turpentine, shake well, and allow the mixture to stand for a day or two, shaking it occasionally. Then add 5 quarts of boiled oil, shake the whole, and allow it to stand in a warm room until clear. This clear portion is then to be poured off for use, and may be reduced in consistency by the addition of turpentine. This varnish is intended for protesting surfaces against the effects of exposure to the atmosphere, and has been used with great advantage for coating wood and iron-work.

Defects in Varnishes and their Remedies. In applying oil varnishes to different objects, various defects often make their appearance, these are in many cases very obscure in their origin, although painfully obvious in their effects. The defects may arise through faults in making the varnishes, through defects in the surface of the objects which have been varnished, through faulty methods of application, or through climatic changes. Seeing, therefore, that there are so many factors which produce defects in varnished surfaces, it is no wonder that the causes of such defects are obscure, especially as the varnisher may be of an unobservant character and fail to notice faults at the time the varnish is being applied. Cracks and pinholes: