Lightfastness is important for artist materials, this video chooses two watercolours from Winsor & Newton to demonstrate how they stand up to the test of light, Alizarin Crimson and Permanent Alizarin Crimson. Alizarin Crimson is based on a lake pigment, which comes from a dye, and Permanent Alizarin Crimson is a modern synthesized version of this colour. A swatch is painted of both, half of the swatch is masked and then it is placed in our lightfast testing machine. We can reproduce the light exposure of 50 to 100 years in a gallery in a matter of hours. As the swatches reveal, the original Alizarin Crimson fades with exposure to light but the modern version is not impacted.