Lightfastness is the ability of a pigment to maintain its color when exposed to the UV rays of sunlight.
Some colors lighten, while other pigments darken or become gray over time.
This changes the artist’s original concept and can ultimately ruin the work.
Pigments
Pigments are organic, mineral or synthetic derivatives and have been used for thousands of years. Natural minerals are the earliest known pigments used, and examples of them can be seen in the Paleolithic and Neolithic cave paintings found in France and Spain.
Mineral pigments generally have a high lightfastness rating. Iron oxide pigments are used to create earthy colors such as dull reds, yellows and browns. These paints, such as rusty red barn paint, are extremely lightfast and inexpensive. That’s the reason that barns have historically been painted red.
Organic pigments do not fare well against the UV rays of the sun. They tend to be fugitive colors that fade significantly over time. Many unfortunate souls have purchased a lovely floral still life bedecked with charming red roses. Fast forward a few years, and those jewel-toned red roses are faded to pale pink or have disappeared completely. Those exquisite roses were probably painted with Rose Madder, which is a pigment made from the madder root.
Today’s technology has produced superior formulations for most paints. These paints are very lightfast and retain their color and vivid tones indefinitely. This is, in great part, due to the automotive industry. Cars need paints that will not fade with exposure to UV rays, so it seems that artists can thank Henry Ford for all their wonderful, lightfast paints.
Lightfastness Ratings
All tubes of paint have lots of information printed on the label. It includes the manufacturer’s name for the color, which is usually translated into several languages. It will include the names of the pigments used to produce the color and their industry-standardized numbers. It may also include other information such as the price group and product code. One thing all manufacturers include is the lightfastness rating.
The lightfastness rating indicates how well a paint will withstand exposure to light. The American Standard Test Measure has a system of rating paints for lightfastness. The British Blue Wool Standard also has a scale for determining lightfastness. The ASTM rates pigments from I to V, while the Blue Wool Standard uses numbers from one to eight to rate permanence.
The ASTM rates pigments as I for excellent durability, II for very good and III for fair or non-permanent. IV and V pigments are rated as poor and very poor.
The Blue Wool Standard rating of one to three indicates the pigment is fugitive and will most likely change color within 20 years. A rating of four or five is fair, and the color should remain stable for 20 to 100 years. Paints rated six have a very good durability. Paints with a rating of seven or eight are excellent, and there is no need for concern of colors fading or degrading.
These ratings allow the artist to judge whether the paint is suitable for its intended use.
Comparison Of The ASTM And Blue Wool Scale
- ASTM I – Blue Wool Scale 7 and 8
- ASTM II – Blue Wool Scale 6
- ASTM III – Blue Wool Scale 4 and 5
- ASTM IV – Blue Wool Scale 2 and 3
- ASTM V – Blue Wool Scale 1
Famous Paintings Faded
Galleries and museums have many paintings by famous artists that have simply faded, darkened or the color has altered over time. Van Gogh’s vibrant yellows have turned brown. A 50-year-old multi-panel mural painted by Mark Rothko has faded from red to blue. J.M.W Turner’s paintings are notoriously faded, as he was quite indifferent to the lightfastness of the paints he used.
If you’re painting short-term, decorative pieces for a display or other temporary work, the lightfastness of the paint should be of no conern. However, if you’re doing serious work, pay attention to the lightfastness of your paints. It would be nice to think that your work will be seen 100 years from now as bold and beautiful as the day you painted it.
