According to the Boston Globe, the primary difference between bronze and brass is that bronze is made from the combination of copper and tin, while brass is made from copper and zinc. Both are copper alloys, meaning that they are mixtures that are in the solid state.
Bronze was first discovered around 3500 B.C. As it is harder than iron and resists corrosion, people of the time began to use bronze to make weapons. This led people to name this time period the Bronze Age. Brass was not discovered for about 3000 more years. This is largely due to the fact that zinc is very difficult to find in its pure form on Earth. To produce the first brass, metallurgists smelted copper with calamine, which is a zinc ore. During the smelting process, the zinc would immediately precipitate from the ore and bond with the copper.
In modern times, copper is mixed with varying amounts of other minerals to produce specialized bronze or brass. These minerals alter the properties of the two alloys, making them harder, softer or less brittle. Because many different minerals are incorporated with copper to make these modern variations, it is often hard to tell the difference between bronze and brass visually.