Blue Wool Standard

Blue Wool Standard Card

Description

[International Standards Organization] A standard used to characterize lightfastness of materials. The Blue Wool Standard consists of a card that contains eight sections of blue-dyed wool cloth, each with a different lightfastness. The dyes fade at a known rate with each section requiring about twice as much light exposure as the preceding section in order to fade to the same degree. Section ISO 1 is the most fugitive and ISO 8 the most stable. In the absence of ultraviolet light, it takes approximately 400,000 lux hours to cause noticeable fading for the ISO 1 level and 900 million lux hours for the ISO 8 level (Michalski 1990).

The internationally recognized standard is not just used for textiles, but also printing inks, polymers, paints, and artist materials. Testing is usually done in an enclosed laboratory using a Xenon arc lamp, which artificially simulates the exact wavelength and intensity of natural daylight alongside regulated humidity. The material is exposed to light concurrently with a standard blue wool textile card. When the test material's color change matches one of the Blue Wool reference swatches, it receives that corresponding number on the scale James Heal.

The Blue Wool Scale originated with the first standards developed in Germany by the Deutsche Echtheitskommission (DEK) in 1914. Building on this foundation, British textile chemists affiliated with the Society of Dyers and Colourists (SDC) further developed the scale in the late 1920s. Negotiations between the Germans and British then standardize the scale which was then adopted by the American Association of Textile Chemists and Colorists (AATCC) in 1940.

Synonyms and Related Terms

Blue Wool Fade Card; ISO Standard R 105; British Standard BS 1006; fading card; norme ISO laine bleue (Fr.)

Physical and Chemical Properties

Standard step parameters:

• ISO 105-B01: fades in about 3-7 hours of sunlight; dye = CI Acid Blue 104
• ISO 105-B02: fades in about 6-15 hours of sunlight; dye = CI Acid Blue 109
• ISO 105-B03: fades in about 12-30 hours of sunlight; dye = CI Acid Blue 83
• ISO 105-B04: fades in about 25-60 hours of sunlight; dye = CI Acid Blue 121
• ISO 105-B05: fades in about 50--120 hours of sunlight; dye = CI Acid Blue 47
• ISO 105-B06: fades in about 100-240 hours of sunlight; dye = CI Acid Blue 23
• ISO 105-B07: fades in about 200-480 hours of sunlight; dye = CI Solubilized Vat Blue 5
• ISO 105-B08: fades in about 400-960 hours of sunlight; dye = CI Solubilized Vat Blue 8

Resources and Citations

• International Standard: ISO 105, part B01: Colour fastness to light
• James Heal: Blue Wool Standards - How to Use
• Grokipedia: Blue Wool Scale accessed July 2026
• S. Michalski, "Time's Effects on Paintings" in Shared Responsibilities. National Gallery of Canada, Ottawa, 1990. p.39-53.
• R.L.Feller, R.Johnston-Feller, "Use of the International Standards Organization's Blue Wool Standards for Exposure to Light" AIC Preprints of Papers presented at the 7th Annual Meeting, Toronto, Canada, 1979.
• R. Feller, "Standards in the evaluation of thermoplastic resin" in ICOM committee for Conservation preprints, 5th Triennial meeting, Zagreb. Paris:ICOM, 1978.
• A. Derbiyshire J. Ashley-Smith "A Proposed Practical Lighting Policy for Works of Art on Paper at the V&A" ICOM preprint, Lyon, France, 1999. p.38-41.
• Conservation Support Systems, Catalog, 1997.