The protection afforded by calcium oxalate against acid rain
Acid rain and marble surfaces
Acid rain is caused by the reaction of water vapor in the atmosphere with pollutant gasses such as nitrogen and sulfur, which make rainwater acidic. This acidic rain causes a lot of damage not only to the ecosystem and our environment, but also to buildings and sculptures that are made from limestone and marble.
Buildings and sculptures that are made from marble or limestone are particularly vulnerable to the erosion and decay caused by acid rain. These materials contain calcite, which dissolves easily in acidic water.
Oxalic acid reacts with the calcium carbonate found in marble, to form calcium oxalate on the marble's surface. Applying this acidic paste on the marble surface by spraying or rubbing will give the marble surface a brilliant shine, as well as protect it from the harmful effects of acidic rain. The film of calcium oxalate that forms on the surface is very resistant to acid rain and can therefore be used to protect wall paintings and sculptures.
Warning - An adult is required for the purposes of handling oxalic acid and gloves should be worn at all times. Oxalic acid can be absorbed through the skin and it will react with calcium in the bloodstream, forming kidney stones.