Thickness measurements of a coating process can be made using various techniques:

1. Optical microscopy: In this method, a microscope is used to view the cross-section of the coating and determine the thickness.
2. X-Ray Fluorescence (XRF): XRF uses X-rays to measure the thickness of a coating. The X-rays penetrate the coating and the substrate and interact with the elements present in the coating and substrate. The intensity of the X-rays emitted by the elements is used to determine the thickness of the coating.
3. Ultrasonic thickness gauges: This technique uses high-frequency sound waves to measure the thickness of a coating. The sound waves are sent through the coating and substrate and the time it takes for the sound wave to travel from one side to the other is used to determine the thickness.
4. Magnetic thickness gauge: This method uses a magnetic field to measure the thickness of the coating. A magnetic field is applied to the coating, and the strength of the magnetic field is measured to determine the thickness of the coating.
5. Beta backscatter: In this method, a radioactive source is used to measure the thickness of a coating. The radioactive source sends beta particles through the coating, and the backscattered beta particles are used to determine the thickness of the coating. This measurement solution is disappearing more and more because of the radiation it emits. This radiation can pose safety problems for people working in a wide radius around it.

The choice of method depends on the type of coating, the substrate, and the desired accuracy of the measurement.

These measurements are important to ensure that the coating meets the desired specifications and thickness requirements.