Test every 15 minutes. Before the soap reaches this stage, it can separate into layers of fat and lye. Simply stir again and recheck for tracing. Two other things can affect detection of the tracing stage are the angle of looking at the soap and poor lighting. Sometimes a soap has traced but due to one of both of these two factors it can be difficult to see.
Soaps containing higher amounts of liquid vegetable oil have tracings more difficult to detect.
Tallow based soaps are one of the best tracers. These fats are added after the trace stage has been achieved. The purpose is to make the soap richer and softer to the skin. There are three main types Essential Oils, Fragrance Oils and Herbs. The latter is the least desirable overall, but it is personal taste.