Coating thickness is the number most often left out of a plating specification and most often argued about afterwards. It's worth pinning down.
Thickness and performance
Decorative chrome is thin. Its job is appearance and tarnish resistance, and the corrosion protection is carried by the nickel underneath. Hard chrome is much thicker, because its job is to survive abrasion and to restore dimension. Specifying "chrome plating, 25 microns" without saying which type will get you a phone call.
Three ways to measure it
- X-ray fluorescence (XRF). Non-destructive, fast, good for production checks. The standard method for most decorative work.
- Cross-section microscopy. Destructive but definitive. Cut the part, mount it, polish it, measure the layer under a microscope. Use this for qualification and for disputes.
- Magnetic or eddy-current gauges. Fast and portable, but substrate dependent and less precise. Fine for a quick check, not for acceptance.
How to write it into the spec
State the thickness range (not a single number), the significant surface where it applies, and the measurement method that governs acceptance. "20 to 30 microns nickel on the significant surface, verified by XRF" is a specification. "Adequate thickness" is a future disagreement. See technology and certification.
FAQ
Is thicker always better?
No. Thicker costs more, can affect fit on threaded or mating features, and beyond a point buys nothing. Match it to the application.
Can you measure coating thickness?
Yes, on request.