Thanks for the update. A couple of weeks ago I had a similar experience. I prepped three bottles with borax and fired one that morning. I thought I’d get to the other 2 on my next 2 firings. The next morning I noticed that both bottles had white streaks. I’m not sure I would have noticed on a clear bottle, but both of these bottles were dark colored. I washed them off and decided not to treat with borax until just before I’m ready to fire.
Your experience has validated mine…