Chemists need ways to find out exactly what elements are in a solid metal. To do this, they can use an AC spark as an energy source. The spark uses a very high voltage that flashes many times every second.
This rapid blasting delivers a massive amount of energy to the sample. It vaporizes a tiny spot on the metal and excites the atoms inside it. These excited atoms then release energy by shining with specific colors of light.
The machine reads this light to figure out which elements are present. Because it uses alternating current, the spark turns on and off very fast. Each tiny flash strikes a brand new spot on the metal surface.
This makes the spark incredibly consistent and reliable for exact measurements. It is much better for finding exact percentages of metals than other older methods. For many decades, spark testing was the absolute standard in the steel industry.
Today, many labs use a modern plasma torch instead. However, spark machines are still used because they are tough and test solid metals directly.