i m doing a big cloissonie piece 25"X20", i applied CMC glue as adhesive, nd seived clear crystal flux, after firing....my flux turned out greenish n some parts were burnt black, i did my cloissonie....bt some parts of metal r still burnt, after applying second layer of flux....so how do i remove the burnt flux or should i continue enamel over it....

So as you write I think your flux shift was to thin, too uneven and/or you fired it too long.
The black spots you must remove until you can see the copper color again. Than you can sieving  or in the wet-technique a new layer of flux apply.
If you have a flex-shaft or a mini-motor you can remove the black-spots (it is copperoxide also called scale) with diamond milling tools. Otherwise you must grinding the copperoxide with Carborundum- or Aluminium-oxide stones away.

I was going to suggest the same, grind out the black / thin areas with a flex shaft / bit and reapply flux to those areas, if possible. 

I guess I have never had that experience, but would not go over burnt anything especially if you are using transparent enamels.  I doubt that the metal is burned (dont' know what you are referring to there)

My advise would be to grind out the burnt stuff and redo.

hey...i finally did my peice after cleaning it with flex shaft...it turned out well.

thank you all..especially Mr. Edmund for ur advise that made my mind clear.

thanx...i did according u said...it really helped me to clean my peice...n i also got aware of a new machine...tool