This section is from the book "The Gardener's Monthly And Horticulturist V22", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
The New York Times says: "Sumac is not a merchantable article until it is properly prepared. The preparation consists of gathering the leaves in July, along with the fine twigs, drying them under cover, threshing them with a flail, sifting out all the coarse stuff, grinding the fine matter into powder under a vertical rolling millstone, and packing in bags of 200 pounds. When gathered at the proper season and prepared in the best manner, American Sumac, even that grown in northern localities and heretofore supposed worthless, is said by tanners to be equal to the best Italian. The trouble is that it is not yet prepared properly nor gathered at a season when its coloring properties are just right, so that it gives a dark shade to the leather, when a clean white shade is desired. For this reason the very best Virginia sumac sells for half the price of the foreign, and New York sumac would be unsalable in the market at any price, because tanners would not dare use it, lest their leather might be spoiled.