What is the best method to test if an iron is hot?

Using a white piece of paper to test if an iron is hot is a practical and effective method. The heat from the iron will cause the paper to becoming discolored or even scorch if the iron is hot enough. This method allows you to visually assess the iron's heat level without risking burns or causing damage to surfaces or yourself, which is particularly important in a salon or beauty environment.

Other methods may not be as safe or reliable. For example, placing an iron on a metal surface could potentially damage both the iron and the surface, and it may not give you accurate feedback about the iron's heat level. Pouring water on the iron can be dangerous and could cause steam burns. Checking with your hands is risky, as it could lead to injury from the heat. Therefore, using a white piece of paper is the most sensible and safe choice to determine if an iron is hot.