The science of conserving fossil remains was in its infancy , and new techniques had to be improvised to deal with what soon became known as " pyrite disease " . Crystalline pyrite in the bones was being oxidized to iron sulphate , accompanied by an increase in volume that caused the remains to crack and crumble . When in the ground , the bones was isolated by anoxic 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 Pauw immediately , in the mine @-@ gallery , red @-@ covered the dug @-@ out fossils with wet clay , sealing them with paper and plaster reinforced by iron rings , forming in total about six hundred transportable blocks with a combined weight of a hundred and thirty tons . In Brussels after opening the plaster he impregnated the bones with boiling gelatine mixed with oil of cloves as a preservative . Removing most of the visible pyrite he then hardened them with hide glue , finishing with a final layer of tin foil . Damage was repaired with papier @-@ mâché . This treatment had the unintended effect of sealing in moisture and extending the period of damage . In 1932 museum director Victor van Straelen 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 gelatine was removed and impregnated with polyvinyl acetate and cyanoacrylate and epoxy glues . Modern treatments of this problem typically involve either monitoring the humidity of fossil storage , or , for fresh specimens , preparing a special coating of polyethylene glycol that is then heated in a vacuum pump , so that moisture is immediately removed and pore spaces are infiltrated with polyethelene glycol to seal and strengthen the fossil .