Lightfastness
Plural: Lightfastness ratings or lightfastness classifications (the noun lightfastness itself is generally uncountable).
Lightfastness definition
Lightfastness is a paint’s ability to resist fading or changing color when exposed to light over time.
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Lightfastness is the degree to which a pigment retains its original color and appearance after prolonged exposure to natural or artificial light. It is one of the most important indicators of a paint’s long-term permanence.
For artists’ paints, lightfastness is commonly measured using standardized tests, such as the ASTM International rating system.
- ASTM Lightfastness I – Excellent. The pigment is extremely stable and suitable for museum-quality, archival, and professional artwork intended to last for generations.
- ASTM Lightfastness I – Excellent. The pigment is extremely stable and suitable for museum-quality, archival, and professional artwork intended to last for generations.
- ASTM Lightfastness III – Fair. Less resistant to fading and generally not recommended for permanent works.
- ASTM Lightfastness IV – Poor. Significant fading can occur with prolonged light exposure.
- ASTM Lightfastness V – Very Poor. Highly prone to fading and unsuitable for artwork intended to be permanent.
Lightfastness refers specifically to how well a pigment withstands light exposure. It should not be confused with other paint properties such as opacity, tinting strength, or permanence of the paint film.
Examples
“This paint is rated ASTM I, so it has excellent lightfastness.” “For professional oil paintings, artists usually choose pigments with ASTM I or ASTM II lightfastness.” “A pigment with poor lightfastness may gradually fade after years of sunlight exposure.”
Context
Lightfastness is one of the key specifications printed on professional paint tubes alongside the pigment code, opacity, transparency, and series number. It helps artists choose pigments that will remain stable over time, ensuring that finished paintings retain their original appearance for decades or even centuries.
Core Principles
- Higher lightfastness means greater resistance to fading.
- ASTM I and ASTM II are considered suitable for permanent works of art.
- Lightfastness measures pigment stability under light exposure, not the durability of the paint film itself.
- Professional artists generally avoid pigments rated ASTM III, IV, or V for archival paintings.
Derivation
The word lightfastness combines light and fast, where fast is an old English term meaning firmly fixed or resistant. The term literally means resistance to the effects of light.