What should be done before starting a chemical service on a client?

Before starting a chemical service on a client, conducting a thorough consultation and performing a patch test are essential steps. The consultation allows the stylist to gather important information about the client's hair type, texture, and any previous chemical services they may have had, which helps to assess potential risks and determine the best service for their needs.

The patch test, on the other hand, is crucial for identifying any allergic reactions to the chemicals that will be used. By applying a small amount of the product to a discreet area of the skin, the stylist can observe for any adverse reactions over a specified period. This step is vital for ensuring the client's safety and preventing any unexpected complications during or after the service.

The other options, while important aspects of overall hair care and service, do not fulfill the critical requirement of ensuring the client's safety and compatibility with the chemical products being applied.