Lightfastnesses

Part of speech: noun

Definitions

1. The ability of a material, especially dyes or pigments, to resist fading or change when exposed to light
2. The property that indicates the stability of colorants against degradation due to exposure to sunlight
3. A measure of how well a substance maintains its original color under prolonged illumination conditions

Etymology: Lightfastness is a compound of "light" and "fast," where "fast" in the old sense means firm, fixed, or resistant to change, as in "colourfast" or the older "fast dye." The word is a technical coinage from the world of dyeing and painting, and it is built entirely from English parts rather than borrowed from Latin or Greek. The plural "lightfastnesses" is simply the noun "lightfastness" with the plural ending, used when comparing the performance of different dyes or pigments. Its base sense, the quality of holding colour under light, is the one that matters for the pigment trade, where manufacturers rate paints by how well they resist fading.