I have slumped many wine bottles and in my opinion you’re making this a little too complicated. Of course there’s many ways of slumping and we all just want to make sure we get good products for our customers in the end.
In my experience, it’s well worth the small amount of money to buy the devit solution. Here’s what i do:
once i get the label off the bottle, i also use Goo Gone if there’s any residue left on the bottle. I clean with windex making sure not to leave any fingerprints on the bottle. I put the bottles in the kiln and then put a LITE coast of Fuse Master Clear Coat on the top of the bottle only. Use sparingly as you don’t want the solution to run down the side of the bottle. If you do it will get on the back of the bottle and will not come off no matter what you do. It will turn white and very hard. I’ve tried drills, files, glass sand paper, dremel and nothing. If someone knows how to get this off i’d love to hear about it…
Anyway, the deal about using borax and waiting a day or so to fire sounds way too complicated and time consuming in my opinion.
I hope this helps. Happy Slumping!