 The science of <unk> fossil remains was in its infancy , and new techniques had to be improvised to deal with what soon became known as " pyrite disease " . <unk> pyrite in the bones was being <unk> to iron <unk> , accompanied by an increase in volume that caused the remains to crack and crumble . When in the ground , the bones were isolated by <unk> moist clay that prevented this from happening , but when removed into the drier open air , the natural chemical conversion began to occur . To limit this effect , De <unk> immediately , in the mine @-@ gallery , re @-@ covered the dug @-@ out fossils with wet clay , sealing them with paper and plaster reinforced by iron rings , forming in total about six hundred <unk> blocks with a combined weight of a hundred and thirty tons . In Brussels after opening the plaster he impregnated the bones with boiling <unk> mixed with oil of <unk> as a <unk> . <unk> most of the visible pyrite he then hardened them with hide glue , finishing with a final layer of tin foil . Damage was repaired with <unk> @-@ <unk> . This treatment had the <unk> effect of sealing in moisture and extending the period of damage . In 1932 museum director Victor van <unk> decided that the specimens had to be completely restored again to safeguard their preservation . From December 1935 to August 1936 the staff at the museum in Brussels treated the problem with a combination of alcohol , arsenic , and 390 kilograms of shellac . This combination was intended to simultaneously penetrate the fossils ( with alcohol ) , prevent the development of mold ( with arsenic ) , and harden them ( with shellac ) . The fossils entered a third round of conservation from 2003 until May 2007 , when the shellac , hide glue and <unk> were removed and impregnated with <unk> acetate and <unk> and <unk> <unk> . Modern treatments of this problem typically involve either monitoring the humidity of fossil storage , or , for fresh specimens , preparing a special coating of <unk> <unk> that is then heated in a vacuum pump , so that moisture is immediately removed and pore spaces are infiltrated with <unk> <unk> to seal and strengthen the fossil . 
