Book 13, Question 43
Why Do Old Posters in Sunny Windows Fade to Blue?
Sunlight, especially ultraviolet light, slowly breaks apart the molecules that give inks and dyes their colors. Some dyes break down faster than others. Often red and yellow fade first, leaving blue behind!
More fun facts
- Light fades, or bleaches, colours, and the most sensitive ones can disappear within as little as a few hours of direct sunshine.
- Many people think ultraviolet causes most fading, but for light sensitive colours it usually causes less than half of it, and often only one tenth.
- Most felt tip pens and most red and blue ballpoint inks are in the group of colours most easily faded by light.
- In average daylight, the most sensitive colours can show a just noticeable fade in anywhere from 1 day to 2 weeks.
- Light damage grows with brightness, so sunlight fades things about 1,000 times faster than good museum lighting.
- Colours that do not fade, like those on ceramics, may last for centuries in direct sunshine.
- There is no true way to bring a faded colour back.
Sources: Canadian Conservation Institute
Questions kids ask
Why does blue often stay when other colours fade?
Each ink fades at its own speed, so the toughest colour is the one left behind.
How can I keep a poster bright?
Hang it out of direct sunlight, or close the blinds when nobody is in the room.