 Certain small areas were left unrestored, in order to maintain a physical record of the previous restorations that had taken place, for example, an area left with overpainting and candle wax, and another area demonstrating the attempt to counteract salination with oil.Once the many layers of candle wax, varnish, and animal glue were removed from the surface of the Sistine Chapel frescoes, they became subject to dangers that could not have been predicted by previous restorers.One of the major dangers to the frescoes is automotive exhaust, and they are also vulnerable to the effects of the crowds of tourists that pass through the chapel every day, bringing with them heat, humidity, dust and bacteria (the latter of which can biodegrade paints and pigments).