In a method of monitoring deposition of a noble metal in an intergranular stress corrosion crack in a metal reactor shroud wall of a nuclear reactor, a metal sample may be placed at a location within near an inner surface of the metal reactor shroud wall. Disclosed are filaments with multiple layers surrounding a core yarn, where the core and layers are distinguishable from one another so as to indicate fabric wear. The sample column may be provided with a reduced-diameter apex at its outward end, e.