[Bunyip]

Yes you can batch anneal boro. For maximum safety never put cold pieces into a hot kiln. However, as noted above Borosilicate glass is far more thermally stable than soft glass. It all comes down to your risk tolerance.

I wouldn't hesitate to put a room temperature 3mm boro rod into a hot kiln, but a 2" marble? Probably not a good idea. Personally, I have not had issues with putting the pendants I make into a hot kiln even after they have cooled.