I just want to highlight today a couple of examples:
- the new Love Pencils - the Derwent blog created by the Cumberland Pencil Company has a post Lightfastness Testing Revealed! about how they test for lightfastness
- Schminke - who make pastels I use - have a two page leaflet about the processes they use when creating art materials (see lightfastness.pdf available to download as a pdf file). In it you can see an example of the blue wool cards used as a quality control by many companies manufacturing art materials. This gives you a very good display of just how much fading happens in those actually graded 'lighfast' at levels 5 and 6 - and just how much disappears at the lower end of the scale.
|Extract from Schminke Leaflet - Lightfastness – A Measure of the Durability of Artists’ Colours (pdf file)|
You can read and learn more about lightfastness on two of my resources for artists sites:
- Pastels - Resources for Artists: Pastels: Technical data about their composition and lightfastness / permanence