Dyed Briollettes


How can you tell if dyed gemstones will fade? I bought a couple of
strands of dyed chalcedony briollette a year ago and half of them
have faded. I asked the vendor if they would faded and of course he
said they would not. Since I now how that the vendors can’t always
be trusted, is there a way to tell if treated stones will fade over
time? Are there any particular types of treatments of treated stones
that I should stay away from?