Does anyone have suggestions on how to remove the hardened flux after brazing? The stuff can be chipped off to some extent, but there is always a small amount left. Also chipping can leave marks in the work piece. I have used a bead blast cabinet in the past but no longer have access. The problem with remaining flux is that after time it absorbs moisture and "puffs up", which makes the work piece look bad at the very least. If you are painting the piece then the paint can be ruined by the flux.
Thanks. Al.

high pressure steam or hot water while cooling
To remove when hardened, Lacquer thinner and toothbrush

Most brazing flux is Borax based.  It becomes a glass or very hard plastic after cooling.
At initial solidification it can generally be dissolved by acid washing.  After aging flux becomes WAR.

When the presence of flux is critical, the usual solution is to over braze and then gring the excess brass with the layer of flux off. Other than that, wire wheel (which will leave marks of course, but finer wheel's will leave finer marks. The only chemicals that come to mind that will touch it are nasty and generally will contaminate what you are working on as badly as the flux...
(Phosphoric acid won't remove flux, but it will inactivate it for certain types of paint.)

Depending on that you are brazing, and how clean it is, you could try a different flux, they make cleanable fluxing compounds for food service etc, but they are weak, the metal has to be clean clean clean....(and if it's that clean you can braze without flux ; P)