1) A fine-grained variety of quartz or jasper which can be used to test the quality of gold and silver alloys. The determining factor is the colour of the mark made when they are rubbed on the stone.
1485 lapis niger vocatus tuche iiijd, Ripon. When the cutler John Shirtcliffe died in 1713 there was a Touch-stone listed in his inventory, worth seven shillings.
2) An official mark or stamp upon gold or silver which indicates that it has been tested, used as a noun or verb.
c.1420 si ascun meistre en dite artifice vende ou mettra a vente ascun choise dore ou dargent que appent a lour dite arte avaunt qil soit touche avec le commune touch de la dite cite ... qil forfaite vjs viijd, York
1443 A quart pot of silver with the touche of Parys, Willoughby, Nottinghamshire
1561 the said goldsmythes sholde bring their towche so that thar work might be approved and towched with the pounce of this Citie, York.