Solubility of Potassium Dichromate is 12.3% @ 20C, from here.

So you are, in fact, right at or above the saturation point. It has nothing to do with the bottle you're storing it in, IMO. This is un-advisable, since you can never be sure what your concentration is, unless every use you make sure to warm it to dissolve all crystals.

If you need a stable solution of that concentration, I'd recommend ammonium dichromate, if your process is compatible with it. (e.g. carbon is OK, but I've never done gum, so I don't know.) It's solubility limit is 35.6% @ 20C.

--Greg