|MadSci Network: Chemistry|
Without getting too technical, just remember that each color is made by using a different dye and therefore a different chemical. The same color on different materials is made from different dyes. Fading is caused by either the breakdown of the dye into smaller chemicals or by just washing the dye from the fabric. The terms for this are lightfastness (resistance to light fading) and wetfastness (resistance to chemicals/washing). When you wash or bleach fabric the dyes can resist the reaction with the bleach or resist washing off at different rates. It is like when you spill mustard on your shirt or get dirt on your pants. Ketchup washes off fairly easy, while dirt is hard to get out. Dyes are very similar. The goal of textile companies is to find dyes that have high fastness (very resistant). These dyes are however more expensive and used only in more expensive clothing. Sometimes you only need one fastness. Take car seats for example. They need to be lightfast (always outside), but not wetfast (never washed).
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