After the excitement of playing with a pile of new art materials dies down, the important job of testing for light fastness must be done. It is a simple task, but takes a couple of months to yield a result. The test involves putting a mark of all the new materials onto a piece of paper. Cutting the paper so that the marks are cut in half, then placing one half behind glass, on a window sill or ledge exposed to the sun and the other half in a book or dark draw. After 2 – 3 months compare the two halves and don’t use any of the products that show signs of fading or color shift.
With the ink marks, a graded dilution with clean water will also show the permanence of thin washes.
Many manufacturers provide light-fastness and permanence ratings on their products, but, for the small effort involved, it is worthwhile checking for yourself.