This section is from the book "The Gardener's Monthly And Horticulturist V23", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
Some one asks what is best for shading a glass house. Mr. Henderson advises naphtha and white lead, mixed to the consistency of milk, and sprinkled on the roof with a syringe. Having tried the experiment, I am satisfied that a thin brush, about three inches wide, is better than a syringe. It is better to spatter it on the roof sidewise from the top of a step-ladder to prevent the material entering the laps and defacing the plants. Zinc would be more transparent than white lead, and I think would do as well.