Definition of "shumac"

In dying a Cotton Gown Black. [...] For a gown, take half a pint of ground shumac and put it into a sieve, and place it in a pan; then pour boiling water on it, and let the shumac water run into the pan; then put in your gown, and let it steep for six hours; [...]

1817, William Tucker, “On Dying Cottons, Dresses, Bed-furniture, &c. &c.”, in The Family Dyer and Scourer; being a Complete Treatise on the Whole Art of Cleaning and Dying: […], London: Printed for Sherwood, Neely, and Jones, […], pages 102–103

Often, on descending into the narrow valleys, we found a little spot of cultivation, a garden, or a field hedged round with shumacs, rhododendrons, and azalias, and a cottage covered with roses.

1832, [Frances Milton] Trollope, chapter XVIII, in Domestic Manners of the Americans. […], London: Printed for Whittaker, Treacher, & Co.; […], page 160

Then lot 1 will be shumacked first time; that is, passed through a decoction of shumac, then through copperas, and then washed off, and if the decoction of shumac is kept up strong, after being all of them once shumacked they may be dried. [...] If the black liquor and the shumacking were powerful, some of them will shew themselves finished when dry.

1816, Thomas Packer, “On Dying Silk Black, According to M. [Pierre] Macquer”, in The Dyer’s Guide; being an Introduction to the Art of Dying […], London: Printed for Sherwood, Neely, and Jones, […], page 90

Harness backs, previous to currying are wetted back in cold or tepid water for skiving; they are then thoroughly scoured, grain well cleaned, and re-shaved, or "flatted" on the flesh if necessary. They are then shumaced to brighten the color. Some makers shumac before flatting in drum tumblers.

1905 July, “Tanning Heavy Leather: Specimen Answers to the Questions Supplied by Dr. J. Gordon Parker of Harold’s Institute, London”, in The Leather Manufacturer: A Technological Journal, volume XVI, part 7, Boston, Mass.: Deming & Rogers, page 115