White layer is not a necessity of nitriding, the qualification of "good" nitriding is with testing the hardness (unless you get into ion nitriding, but that is different from your situation I think).
You might want to try Ultrasonic Contact Impedance (UCI) probes, which can read in vickers...
mfgenggear - Impossible... If you are talking about copper sulphate (CuSO4).
Fe+CuSO4 --> FeSO4+Cu therefore only bare Fe will result in Cu deposition.
You must be thinking of cupric ammonium-chloride
Cu(NH4Cl)2
I prefer to use copper(II) chloride dihydrate power mixed to saturation in DI...
Huh??
mfgenggear - depending on surface prep, concentration and time on surface, the copper sulphate may or may not deposit Cu on a white layer. A smooth, low porosity white layer will RESIST copper sulphate to a high degree.
Also, if you are spot testing a 1.5m dia gear, nital won't hurt...
