▁sense , ▁rec y cling ▁of ▁a ▁material ▁would ▁produce ▁a ▁fresh ▁supply ▁of ▁the ▁same ▁material — for ▁example , ▁used ▁office ▁paper ▁would ▁be ▁converted ▁into ▁new ▁office ▁paper ▁or ▁used ▁pol yst y rene ▁fo am ▁into ▁new ▁pol yst y rene . ▁This ▁is ▁accomplished ▁when ▁rec y cling ▁certain ▁types ▁of ▁materials , ▁such ▁as ▁metal ▁can s , ▁which ▁can ▁become ▁a ▁can ▁again ▁and ▁again , ▁in def initely , ▁without ▁losing ▁pur ity ▁in ▁the ▁product . ▁However , ▁this ▁is ▁often ▁difficult ▁or ▁too ▁expensive ▁( comp ared ▁with ▁producing ▁the ▁same ▁product ▁from ▁raw ▁materials ▁or ▁other ▁sources ), ▁so ▁" re cy cling " ▁of ▁many ▁products ▁or ▁materials ▁involves ▁their ▁reuse ▁in ▁producing ▁different ▁materials ▁( for ▁example , ▁paper board ) ▁instead . ▁Another ▁form ▁of ▁rec y cling ▁is ▁the ▁salv age ▁of ▁certain ▁materials ▁from ▁complex ▁products , ▁either ▁due ▁to ▁their ▁intr insic ▁value ▁( such ▁as ▁lead ▁from ▁car ▁batter ies , ▁or ▁gold ▁from ▁printed ▁circuit ▁bo ards ), ▁or ▁due ▁to ▁their ▁ha z ard ous ▁nature ▁( e . g ., ▁removal ▁and ▁reuse ▁of ▁mer cur y ▁from ▁therm om eters ▁and ▁therm ost ats ). ▁ ▁History ▁ ▁Orig ins ▁ ▁Rec y cling ▁has ▁been ▁a ▁common ▁practice ▁for ▁most ▁of ▁human ▁history , ▁with ▁recorded ▁advoc ates ▁as ▁far ▁back ▁as ▁Pl ato ▁in ▁the ▁fourth ▁century ▁BC . ▁During ▁periods ▁when ▁resources ▁were ▁scar ce ▁and ▁hard ▁to