“…The refractory core tends to be a foil that is 20-30 lm [143,[207][208][209][210][211][212][213][214] or 100-127 lm thick [116,188,189,201,207,[211][212][213][215][216][217][218][219][220][221][222], although it can be in the 200-1000 lm range [202-205, 208, 223-225]. The refractory core element is often Ni [144, 189, 196, 201-204, 207-210, 218, 224, 226, 227]; other elements (and an alloy) that have been used include Au, Co, Cu, Nb, Ni-Cr, Pd, Pt, Si, Ta, Ti, and V [117, 188, 189, 200-202, 205-208, 214-218, 222, 227-229].…”