Patent ID: 6903339

Claim:
A non-destructive method of determining an amount of opaque coating on a substrate, the method comprising: non-destructively determining a value A1 of absorbance of infrared energy at a first wavelength in an opaque coating on a substrate, wherein the value A1 is a selected function of a ratio that includes a value I c1 of infrared energy at the first wavelength that is scattered by the opaque coating divided by a value I o1 of infrared energy at the first wavelength that is scattered by a reference substrate without the opaque coating; non-destructively determining a value A2 of absorbance of infrared energy at a second wavelength in the opaque coating on the substrate, wherein the value A2 is a selected function of a value I c1 of infrared energy at the first wavelength that is scattered by the opaque coating divided by a value I c2 of infrared energy at the second wavelength that is scattered by the opaque coating; and correlating a difference A1−A2 to an amount of the opaque coating.