The issue has been the preservation of over 2,000 works of paleolithic art. The cave itself was discovered by teenagers in 1940 and thereafter was opened as a public exhibit; however the roughly 1200 visitors per day created an immense accumulation of carbon dioxide which damaged the figures and led to the closing of the cave. Aside from carbon dioxide, an air conditioning system was added to the caves which changed the degree of humidity present which together with light emitted by the lighting system encouraged the growth of black mold. This led to closing of the caves and attempts to remove the mold; unfortunately new forms of mold have appeared and the process of removing it is tedious and time consuming. There is no guarantee that the fungi can be safely and completely removed.