Engine knocking is reduced by the use of a manganese compound in unleaded gasoline (also called petrol). This boosts the fuel’s octane rating. Manganese is used in standard disposable batteries, but this use is becoming less common as lithium battery technology improves. Manganese is essential in the production of steel and iron and this makes up the most common use of this metal. It improves the workability of the steel when it reaches high temperatures. Adding about 8-15% of manganese also increases the strength of the steel. It is also a vital component of lower cost stainless steels. The second largest use of manganese is creating an alloy with aluminum to produce a metal that is more resistant to corrosion. Most aluminum beverage cans contain about 0.8 to 1.5% of manganese. In the chemistry laboratory, manganese (IV) oxide is used to oxidize benzylic (cyclic) alcohols. Iron contamination can give glass a green tinge. A compound of manganese has been added to glass since ancient times to counteract this effect. Oxygen and chlorine are manufactured using manganese dioxide. This same compound is also a brown pigment that can be used to make paint. Glass and ceramics can be colored by using various compounds of manganese. In some parts of the world, manganese is used in monetary coins. Since 2000, it has been alloyed with other metals in the United States for some dollar coins, such as the Sacagawea dollar and the Presidential dollar coin.