Non-destructive method of determining the refractive index of clear coats

A method for determining repairabilitly of an original clear coat applied over a darkly pigmented substrate with a corresponding repair clear coat, said method comprises:

• A) non-destructively determining the refractive indices of the original clear coat and the corresponding repair clear coat by the steps comprising:
• I) acquiring the reflection spectrum of the original clear coat and the corresponding repair clear coat obtained with a spectrophotometer with d/8° measurement geometry with the specular component included and with the specular component excluded;
• II) determining the differential spectrum between the reflection spectrum with the specular component included and reflection spectrum with the specular component excluded;
• and
• III) determining the refractive index of the original clear coat and the corresponding repair clear coat with the assistance of the differential spectrum obtained in II) by making use of a previously determined relationship between the difference in the reflection spectrum with the specular component included and the reflection spectrum with the specular component excluded of the original clear coat and the corresponding repair clear coat;
• and
• B) comparing the refractive index of the original clear coat and the repair clear coat to determine difference between the refractive indices of the original and repair clear coats, wherein when said difference between the refractive indices of the original and repair clear coats is within an acceptable range, the repair clear coat is used to repair the original clear coat.