[Twigg]

I have an amber boston round bottle which used to hold DPIP. The DPIP became contaminated last year; there was a dense murky purple precipitate, probably from the spinach extract I had been adding the DPIP to. Of course, I left the solution in the bottle in a corner of my storage cabinet for a year. After reading the MSDS and getting advice, I disposed of the solution down the drain with plenty of water.
The problem is, the bottle has been stained on one side. I rinsed it with hand soap and water for fifteen minutes, but it still didn't come off. I could get a replacement cheap, but is there any simple way to clean the stains? I'd hate to throw out such a nice bottle for a little stain.

[Stepan]

Alkaline solution may work. Let it stay with NaOH overnight. NaOH dissolves glass layer under the stain and it peels off. Bleach might work as well.