two metal elements may have a lower ionization potential than the first metal element the combination of metals metal elements used to obtain the starter material alloy for the core can be one in which the metal have different chemical properties so as to allow for dealloying examples of metal elements include elements selected from the group consisting of transition metal elements typical metal elements and the like for example iron group elements platinum group elements copper group elements zinc group elements aluminum group elements manganese group elements chromium group elements earth acid elements titanium group elements rare earth elements alkali earth metal elements alkali metal elements lanthanide elements actinide elements tin lead germanium bismuth antimony and the like the alloy may contain a typical non metal element examples including carbon group elements nitrogen group elements oxygen group elements halogens boron and the like suitable alloys are not limited thereto and may include constituents selected as appropriate from among those known to a person skilled in the relevant field of art such as gold au silver ag copper cu zinc zn aluminum al nickel ni tin sn manganese mn iron fe cobalt co chromium cr molybdenum mo tungsten w vanadium v niobium nb titanium ti zirconium zr magnesium mg platinum pt palladium pd ruthenium ru rhodium rh osmium os iridium ir and the like more specific examples of alloys include au u2014 ag alloys au u2014 cu alloys cu u2014 mn alloys cu u2014 al alloys cu u2014 zn alloys cu u2014 mg alloys ni u2014 al alloys ni u2014 mg alloys ni u2014 mn alloys cu u2014 cr alloys sn u2014 pb alloys sn u2014 in alloys ag u2014 cu alloys au u2014 ni alloys au u2014 pd alloys and the like preferred alloys that.