There are many technical terms used to describe the properties of Paint. A little chemistry know-how can help you become a better painter—but don’t worry—we’re not talking about balancing chemical equations or memorizing the periodic table here! This ongoing series of mini-articles will help you get to know your medium on a deeper level.

What is Lightfastness?

Have you ever left construction paper near a sunny window and found that the color became faded in months or even weeks? Maybe you’ve left a plastic item in your yard, or a magazine in your car and later found it bleached by the sun.

Pigments, paper, plastic toys, fabric, paint and other items react to sunlight in different ways. Materials that maintain their colors over time are called “lightfast” and Lightfastness can be important when purchasing art supplies.

Some pigments and paints are described as being lightfast because these products are resistant to fading from light exposure. Art products that have a lightfastness rating of “A” are super resistant to fading from light exposure and will not incur color change or fading for up to 100 years when stored in museum conditions. Of course, artwork should not be stored in direct sunlight and is best stored in temperate, low-humidity environments like an air-conditioned home or gallery.

In the textile dyeing and printing industries, The Blue Wool Scale, a scale from 0-8 is often used to describe lightfastness. Those working in fiber arts should be more familiar with this scale than painters.

The American Society for Testing and Materials Standard (ASTM) lightfastness scale is used across many pigmented art materials: ASTM I indicates excellent lightfastness, ASTM II is very good lightfastness, and ASTM III is not lightfast enough to be classified as artists’ quality. Atelier acrylics are example of a paint brand using ASTM to indicate lightfastness. Some product lines use their own scale to indicate levels of light resistance—for example, Royal Talens uses + signs to indicate lightfastness in its products . In the Royal Talens scale, 0 is the least lightfast and +++ is the highest.

Inks, colored pencils and pastels are more likely to fade over time than watercolors, oils and acrylics. If you are trying to create professional work with these drawing mediums it is definitely a good idea to look for products that rate lightfastness or are labeled as being “archival quality.” The way pastels and colored pencils are manufactured and composed chemically makes it so that they have a tendency to fade more quickly than other mediums. Generally speaking, Red Violets are notorious for fading quickly—always look for highly rated Red Violets. Purple is also a tricky color to maintain over time.

Single-pigment paints are generally more lightfast because there is only one pigment suspended in the binder. When there are two or more pigments, each pigment may degrade a different rate, making the color less stable over time.

But all is not lost if you have created a masterpiece with non-lightfast mediums! In fact, due to the difficulty of controlling lightfastness experiments, and the infrequency of such tests, lightfastness is only one indicator of paint quality and staying power. Lightfastness is just one property that can show you the quality of your paint.

The bottom line of lightfastness is this: use quality mediums and take care of your paintings by storing them properly. That is the best thing you can do to keep your colors vibrant over the years.

Even art with lower lightfastness will stay truer and more vibrant over time when stored properly, compared to art made with high quality materials and stored improperly. Artwork should never be stored in direct sunlight and should generally be kept in a temperate, low-humidity environment to preserve all aspects of your painting.

If you’re a fan of Winsor & Newton products and want and overview of their paints’ lightfastness, permanence, and other markers of paint quality, their website has informative charts about each of these paint quality indicators: