This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
Locksmiths and others, says the Home Companion, working at the forge are accustomed to blacken the articles intended for railroads by making them red-hot, and burning on them some linseed oil. This plan, which is practised to improve the appearance of the articles and to protect them from rusting; is not economical nor always successful; it fails when the combustion of the oil has been too great By the following process a varnish is made without the above disadvantages, which gives to the articles a better appearance: Dissolve, in about two pounds of tar-oil, something more than half a pound of asphaltum, and a like quantity of pounded resin; the mixing is performed hot in an iron kettle, care being taken to prevent any contact with the flame. When cold the varnish is poured into a vessel and kept for use. These varnishes are for out-door wood and iron-work, not for japanning, leather, or cloth. Oil varnishes are used for patent leather, and copal for japanning metal - Builder, in London Gardeners' Chronicle.