Definition of "sumaching"

Once during the process of sumaching the skins are removed from the tub and placed on a rack or perforated bench at the side: they are heaped one on another, and by their own weight press all the sumach solution through the pores. Another sumaching and another pressing complete the operation.

1843, George Dodd, “A Day at a Leather-factory”, in Days at the Factories; or, The Manufacturing Industry of Great Britain Described, […] (Series I (London)), London: Charles Knight & Co., […], page 171