How do I set dyed fabric that has been batik so I won't loose the brilliant color?
You require a Mordant http://en.wikipedia.org/wiki/Mordant Alum and urine are 2 common ones. :-)
Salt (sodium chloride) is another. Which is best depends on the specific dyes being used. Check their instructions, and/or search the web for information about that dye.Note that many dyes -- especially natural dies, but not only those -- will fade over time, especially if exposed to a lot of ultraviolet light. If you're worried about this, you may want to try to limit how much time the fabric spends in bright sunlight.