itor ▁to ▁the ▁mine . ▁ ▁The ▁plants ▁were ▁fund ed ▁by ▁French ▁banks ▁and ▁used ▁a ▁novel ▁technology ▁for ▁producing ▁artificial ▁fert il izer ▁by ▁taking ▁nit ro gen ▁from ▁the ▁air . ▁ ▁Though ▁these ▁plants ▁used ▁a ▁lot ▁of ▁energy , ▁Norway ' s ▁natural ▁capacity ▁for ▁hydro elect ric ▁power ▁made ▁them ▁a ▁very ▁effective ▁substitute ▁for ▁ph osph ate ▁min ing . ▁ ▁During ▁w art ime , ▁there ▁was ▁need ▁for ▁even ▁the ▁less ▁efficient ▁methods ▁of ▁fert il izer ▁production , ▁and ▁the ▁Great ▁War ▁represented ▁one ▁of ▁the ▁most ▁product ive ▁periods ▁in ▁ Ø deg år den ▁Ver k ' s ▁history . ▁ ▁However , ▁after ▁the ▁end ▁of ▁the ▁war , ▁ Ø deg år den ▁Ver k ▁found ▁it ▁difficult ▁to ▁comp ete , ▁and ▁B am ble ▁A pat itt ▁A / S ▁declared ▁bank rupt cy ▁in ▁ 1 9 2 0 . ▁ ▁H å kon ▁Math iesen ▁once ▁again ▁took ▁ownership ▁of ▁the ▁mine ▁and ▁ran ▁it ▁himself ▁until ▁its ▁closing ▁in ▁ 1 9 2 6 . ▁ ▁It ▁wasn ' t ▁until ▁World ▁War ▁II ▁that ▁the ▁mines ▁were ▁re open ed . ▁ ▁In ▁ 1 9 4 1 , ▁Adam ▁Pet ter son ▁bought ▁the ▁mine ▁and ▁restored ▁min ing ▁operations . ▁ ▁The ▁newly ▁opened ▁mine ▁proved ▁to ▁be ▁not ▁very ▁successful , ▁and ▁it ▁was ▁closed ▁by ▁the ▁end ▁of ▁the ▁war ▁in ▁ 1 9 4 5 . ▁ ▁Rec