{"id":73164,"date":"2026-04-13T11:15:00","date_gmt":"2026-04-13T08:15:00","guid":{"rendered":"https:\/\/www.artcolour.gr\/?p=73164"},"modified":"2026-04-17T21:06:24","modified_gmt":"2026-04-17T18:06:24","slug":"understanding-lightfastness","status":"publish","type":"post","link":"https:\/\/www.artcolour.gr\/en\/materials-and-guides\/understanding-lightfastness\/","title":{"rendered":"Understanding Lightfastness"},"content":{"rendered":"\n

Have you ever wondered why some colours differ from their original shade after a while? This article explains lightfastness<\/strong>, a very important property of artist paints. <\/p>\n\n

Every tube of paint carries technical information about the colour inside. Among transparency ratings and pigment codes, you’ll find a lightfastness rating, a measure of how that particular pigment behaves when exposed to light over time. Lightfastness has nothing to do with paint quality. It’s a natural characteristic of the pigment itself, like transparency or opacity. Some pigments remain stable for centuries. Others change more quickly. Understanding these differences helps you choose the right materials for each creation. <\/p>\n\n

How Lightfastness Works<\/h2>\n\n

Light carries energy. When it strikes a painted surface, ultraviolet wavelengths can break down the molecular structure of certain pigments. This causes colour change, sometimes subtle, sometimes more pronounced. <\/p>\n\n

The speed and degree of this change depends on the pigment’s chemical composition. For example, earth pigments from iron oxides are exceptionally stable. They come from minerals that have survived geological time unchanged. Some organic pigments, composed of carbon compounds, have molecular structures more vulnerable to UV energy. <\/p>\n\n

This isn’t a flaw. It’s simply their chemistry. <\/p>\n\n

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Comparison showing the different behaviour of the same colours without sun exposure (top) and after sun exposure (bottom)<\/figcaption><\/figure>\n\n

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How to Read Lightfastness Ratings<\/h2>\n\n

Manufacturers test pigments under controlled light exposure and report results using standardised systems. The most common are ASTM and Blue Wool Scale, though some manufacturers use their own notation. <\/p>\n\n

ASTM System (American Society for Testing and Materials)<\/strong><\/p>\n\n

I: Excellent lightfastnessII: Very good lightfastnessIII: Not recommended for professional use<\/p>\n\n

Blue Wool Scale<\/strong><\/p>\n\n

8-7: High lightfastness6-5: Moderate lightfastness4-1: Lower lightfastness<\/p>\n\n

Royal Talens System (used on brands like Rembrandt<\/a> and Van Gogh<\/a>)<\/strong><\/p>\n\n

+++: At least 100 years under museum conditions++: 25-100 years under museum conditions+: 10-25 years under museum conditions\u00ba: 0-10 years under museum conditions<\/p>\n\n

Museum conditions mean controlled temperature, limited light exposure, and protection from environmental factors. Your artwork experiences different conditions, but these ratings provide relative comparison. <\/p>\n\n

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Paints from major manufacturers showing lightfastness markings<\/figcaption><\/figure>\n\n

Pigment Chemistry Matters<\/h2>\n\n

Inorganic pigments come from minerals such as iron oxides, cadmium compounds, cobalt, chromium, and titanium. Their molecular structures tend to be exceptionally stable when exposed to light. Examples include:<\/strong><\/p>\n\n