Painting and preserving iron work.

Scientific American 16, 18.4.1868

A good black paint for coarse iron work may be made by mixing plumbago with hot coal tar. Equal parts of asphaltum and resin dissolved in common turpentine make also a good, cheap covering for heavy iron work.

For machinery, dissolve 2 pounds India rubber, 4 pounds resin, and 2 pounds shellac, in 5 gallons of benzine. This may be used with any other paint as a vehicle.

Wrought iron bridges are painted with white lead as follows: The iron work is first made clean by scrubbing and brushing it with wire brushes; this done, all the cavities and fissures are filled up with a putty of litharge, linseed oil, varnish, and white lead; this filling being dry, brushing is repeated. Afterward, a paint is applied, consisting of 300 pounds of white lead, 10 gallons crude, 1 or 2 gallons boiled linseed oil, and 11 gallons of turpentine. This paint is repeated when sufficiently dry, and finally evenly overspread with white sand.

Galvanizing is employed also to prevent rusting. I have found a galvanizing paint in the trade, consisting chiefly of zinc powder and oil varnish. Rusting is further prevented by rubbing the red hot iron with wax, tallow, pitch, or coal tar.

Rubbing with heavy petroleum is also well adapted for keeping iron work clean.

The common varnish is obtained by adding at 280° some dried sulphate of zinc to boiled linseed oil — take one ounce for one gallon; a better kind is made by boiling 7 gallons of the former with 3 pounds of litharge and 2½ pounds of wax, until thick; when sufficiently cool and settled, the liquor is poured from the remainder.

Copal varnish is prepared by mixing 7 pounds of fused copal with 2/3 gallons of hot drying oil, thinning it off with 4 gallons of turpentine, and straining through a wire sieve of proper fineness.

Amber varnish: Fuse 6 pounds of amber in an iron pot, and pour in 2¼ gallons of hot clarified oil; boil it until it can be drawn out into a stringy mass, and mix with it 5 1/3 gallons of turpentine.

Black iron work varnish: Put 48 pounds of asphaltum in an iron kettle, and boil it for four hours. During the first two hours, introduce 7 pounds of red lead, 7 pounds of litharge, 3 pounds of sulphate of zinc, and 12 gallons of boiled oil. Continue the boiling for two hours, and when cool thin it off with 40 gallons of turpentine.

Another recipe: Add gradually to 7 gallons of crude oil at a gentle heat, 10 pounds asphaltum in three gallons of hot oil; by stirring continually, add 7 pounds of litharge, 7 pounds of red lead, 3 of sulphate of zinc, and boil for three hours; let cool, and thin off with 40 gallons of turpentine, and strain finally through a fine sieve.

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