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; [...]

Source: wiktionary

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.

Source: wiktionary

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.

Source: wiktionary

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.

Source: wiktionary