Lightfastness Testing Revealed! Nov 2010

Ever wanted to know how we test our pencils for lightfastness? Well, Angela Eland from our laboratory explains how:


“A lightfastness test is a measure of how quickly something will fade when exposed to UV light (sunlight). There is a standard test that has been used for many years called the Blue Wool Scale.

Here at Derwent we use a lightfast machine to test all our ranges of pencils and because we are continuously improving our products with the use of different raw materials we test the pencils for lightfastness every time a change is made.

The machine we use has a light that replicates intense Florida sunshine. We place two identical samples into the machine one sample used as a control is covered by a metal strip so that no light can affect it and the other sample is placed in the ‘sunlight’ for 3 months in total. A standard blue wool card is placed in the machine under the same conditions as the sample.

The blue wool shade card has 8 different pieces of blue wool which fade according to the length of time under the intense light. The amount of fading of the sample is then assessed by comparison to the original colour; a rating of 1 to 8 is awarded by identifying which one of the 8 strips on the blue wool standard card has faded to the same extent as the sample under test.”

It’s just fascinating! We think that the lightfastness machine looks like some sort of space ship! It’s amazing how many quality tests we do here at Derwent; keep your eyes peeled for more features on our lab.