Testing the colourfastness of materials
One of the most important tests for a curtain is colourfastness in sunlight, that is, how it is faded by the sun. The method we use to determine the colourfastness of a material is by using Xenon arc lamp to mimic the sun's rays and in order to make as fair an assessment as possible, the tests are always carried out in light boxes. Because textiles for indoor use are being tested, the standard is adapted to give the same effect as the sun’s rays through a 3 mm single glazed window. During the test, parts of the material are covered with a mask to demonstrate clearly how the material is faded.
The material being tested is then compared to standard fabrics, on what is known as the standard blue wool scale. It consists of 8 blue standardized wool fabrics with varying degrees of light resistance, with 8 being the highest.