Coating with optical taggent

A method for determining the thickness on a metal substrate of a curable or dryable film-forming coating comprising a fluorescent component, comprising the steps of:

• a. determining a mathematical relationship between the fluorescence intensity of the coating when the coating is exposed to light which causes the fluorescent component to fluoresce, versus the coating thickness of the coating when the coating is applied to a substrate by:
• i. coating two or more substrate samples with the coating at two or more thicknesses;
• ii. measuring the fluorescence intensity of each sample when exposed to light which causes the fluorescent component to fluoresce;
• iii. measuring the thickness of the coating for each sample;
• and
• iv. determining the mathematical relationship between the fluorescence intensity of each coating as compared to the thickness of each coating, wherein the fluorescence of the coating composition increases as a function of increasing thickness of the coating composition;
• b. measuring the fluorescence intensity of the coating on a test substrate when exposed to the light;
• and
• c. determining the thickness of the coating on the test substrate by reference to the mathematical relationship.

A method for determining the thickness on a metal substrate of a curable or dryable film-forming coating comprising an organic resin having a fluorescent tag covalently linked thereto, comprising the steps of:

• a. determining a mathematical relationship between the fluorescent intensity of the coating when the coating is exposed to light which causes the fluorescent tag to fluoresce, versus the coating thickness for the coating when the coating is applied to a substrate, wherein the fluorescence of the coating increases as a function of increasing thickness of the coating;
• b. measuring the fluorescence intensity of the coating on a test substrate when exposed to the light;
• and
• c. determining the thickness of the coating on the test substrate by reference to the mathematical relationship between fluorescence intensity and thickness of the coating.

A method for determining the thickness on a metal substrate of a curable or dryable film-forming coating comprising an organic resin having a fluorescent xanthene dye covalently linked thereto, comprising the steps of:

• a. determining a mathematical relationship between the fluorescence intensity of the coating when the coating is exposed to light which causes the xanthene dye to fluoresce, versus the coating thickness of the coating;
• b. measuring the fluorescence intensity of the coating on a test substrate when exposed to light;
• c. determining the thickness of the coating on the test substrate by reference to the mathematical relationship between fluorescence intensity and thickness of the coating, wherein the fluorescence of the coating increases as a function of increasing thickness of the coating and further
• wherein the xanthene dye is present in the coating at 1 ppm to 2,000 ppm of the solids content of the coating.