Anything metalic would usually be removed from the deceased before they are put into the furnace if possible, surgical implants, jewellery,etc.... Deceased Patients in Hospital with pacemakers in will have them removed prior to leaving the mortuary by a pathologist/technician before cremation due to the risk of explosion. Obviously some minor metals can still be burnt or left like dental fillings,known sharpnel etc.. as it would melt down to a small size. Then usually all left pieces would be consecrated in the grounds of the Cremetorium/Cemetery. Hope this helps