What is the difference between impurities and additives in alloys?

Impurities in the alloy are those that cannot or need not be removed, as there is no particular need for this. The reason is the high cost of the process and inexpediency, since the metal alloy can be used in various industries. Impurities do not always affect the quality of the alloy, however, with an increase in the quantitative concentration of certain substances or metals, the properties of the alloy change. As for additives, these are specially introduced substances that contribute to a change in the basic properties of the alloy, for example, color, refractoriness, melting point, and so on.