This paper describes the five-year Lightfastness Correlation Project that I am conducting in sixteen institutions in the US and Western Europe, with the support of the Samuel H. Kress Foundation.
Dr. Robert L. Feller, a scientist at the National Gallery of Art, published several papers in the 1970s in which he speculated that a certain duration of time could be correlated, in a general way, to the color changes noted in the Blue Wool Textile Fading Cards. Museums use the cards as inexpensive dosimeters, put somewhere in a gallery along with the art. Enough is known about their behavior to have confidence in their ability to indicate when it is time to remove an object from exhibition.
The Blue Wools are also used in two Standards developed by ASTM International’s Subcommittee D01.57 on Artists’ Paints and Related Materials. ASTM D 5383 and ASTM D 5398 are simple lightfastness test methods. In them, the Blue Wool cards are exposed to natural daylight along with any colored material, and are used to tell the artist when it’s time to stop the test and as a rating device.
Another ASTM Standard from D01.57, ASTM D4303, uses instruments to control the accumulated amount of natural daylight, or simulated daylight in a xenon arc light exposure machine. It also uses a spectrophotometer to calculate the color change that can occur in a test sample, expressed in CIE L*a*b*. There is also a standard formula for calculating color change that results in a single number, expressed as Delta E, or ∆E.
The ∆E number is used by ASTM D01.57 to assign lightfastness ratings to artists’ coloring materials covered by its Specifications for various products. Initial development of the ASTM methods began in 1977; we have 33 years of data that confirms the worth of the methods used in our testing.
What is the relationship between the results of Blue Wool testing and the results using D01.57’s technical ∆Es? This is a fundamental question we have yet to thoroughly examine. We have begun to work on the problem, using accelerated natural and artificial light sources as in ASTM D 4303. But no one has ever tried to compare the results of these two test methods in a museum environment, over an extended period of real time.
“The Lightfastness Correlation Project” ends in August 2011, and a final scientific report will be submitted to the sponsor, The Samuel H. Kress Foundation, in September 2011.