When performing a metallic test, how long should at least 20 strands of hair be immersed in the mixture?

When performing a metallic test, immersing at least 20 strands of hair in the testing mixture for 30 minutes is essential to ensure accurate results. This duration allows sufficient time for any metallic substances present in the hair to react with the testing solution, thereby producing clear and observable outcomes indicative of any metal presence.

A shorter immersion time, such as 10 or 20 minutes, may not provide enough opportunity for the metals to fully interact with the mixture, potentially leading to inconclusive results. Similarly, immersing the hair for too long, like 40 minutes, may not yield additional benefits and could complicate the interpretation of the results. Thus, a 30-minute duration strikes an appropriate balance for effective testing in a professional setting.