I dont know if it matters with the browning solution, but Ive had cold blue solution be negatively affected when you get anything that touched the metal in contact with the remaining solution in the bottle. I now dump some in the cap, use q-tips or whatever to apply, toss each one as its used, avoid contacting the solution with a used q-tip or patch or whatever, and I toss whatever is left in the cap when done in case I inadvertently made contact. The remaining solution seems to stay good for extended periods.
Ive had poor results when the solution was contaminated, and heard its not good to let the solution come in contact with anything thats touched the work. I dont know positively if its true, but once I started being careful to keep the unused stuff away from the solution I was working with it doesnt seem to go bad or give flaky results any more.