MadSci Network: Chemistry

Re: Why do colors fade at different rates?

Date: Sat Apr 8 22:35:20 2000
Posted By: Henry Boyter, Senior Scientist
Area of science: Chemistry
ID: 954812105.Ch

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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