We take lightfastness very seriously at Derwent as it is vitally important to professional artists. Derwent have the latest testing technology which measures the lightfast levels of every pencil. The pigments used in Derwent products are tested for lightfastness and graded from 1-8 (8 being considered extremely lightfast). We use the Blue Wool Scale, which is a testing standard common with artists' materials manufacturers.
Blue wool ref 1 will fade very quickly, whereas blue wool ref 8 is considered extremely lightfast. Any result above Blue Wool 6 (ASTM II) is considered to be VERY GOOD and will not fade for over 100 years in gallery conditions.
Blue Wool Scale Rating
3, 4 Fair, moderate
5, 6 Good, very good
We constantly monitor, develop and retest our pencil range to improve on our lightfast ratings.