Architectural Paint Investigation – Ultraviolet Examination
Cross-section examination (with Ultra-violet Fluorescence)
The examination of paint samples mounted in cross-section at high magnification under incident (normal) light and ultra-violet illumination can be very informative.
Every paint layer is evidence of a decision to alter an interior – and an indication of the taste, aspirations and wealth of the occupants.
Post WWII alkyd-resin and vinyl-emulsion paints can readily be distinguished from lead-based paints under ultra-violet illumination. Layers of applied varnishes appear as distinctive white layers when viewed under ultra-violet light.
This paint sample taken from a 19th century lamp-post reveals the two early varnish layers and the more recent post WWII schemes.
Zinc white was a pigment commonly used by housepainters from the mid 19th century, but fell out use in the early 20th century. When viewed under ultra-violet light zinc white exhibits a bright sparkly appearance.
This means that it is a useful marker material for the dating of paint. The distinctive white particles in the second decorative of the cross-section below are particles zinc oxide.