 In the first case , acetic acid reacts with the calcium carbonate ( one of the main components of freshwater , marine and land shells , birds ' eggs and other such specimens ) producing calcium acetate , a salt . Formaldehyde can be oxidized by the oxygen in air to create formic acid , which then has basically the same effects as acetic acid , reacting with calcium carbonate to produce a salt . The salts ( calcium acetate and calcium formate ) crystallize through the specimen 's outer surface , destroying its fine detail and exposing more areas for further reaction . As the condition progresses , the salt crystals build up over the specimen 's surface , which becomes increasingly eroded . 
