Today I had a question form my student about lightfastness - I must to admit that aways had a vague understanding of that term. Here is an answer.
"Lightfastness of a paint color or pigment is very important! It indicates how permanent, resistant to change, or how unaffected by light it is. Paint colors can fade or alter when exposed to light and time. This could change the look and quality of an art work.
The two most used rating systems are the ASTM and the Blue Wool Systems. The American Standard Test Measure (ASTM) gives ratings from I to V. (I excellent, II very good, III fair or non-permanent, IV and V poor and very poor).The British system (Blue Wool Standard) rates lightfastness One to Eight. (Eight being Excellent and One being the worst). "
Speaking of light...My Monday pleinair class started two weeks ago and it's going very well.
I can see how some of my students mood and attitude changing from being terrified and self-conscious of painting outside on public to just having fun and letting go the fears of failure or pressure.
Let me know if you are interested.