This part is tough. While the pipe is in the glory hole, you must continuously turn the pipe to keep the glass blob on top. But not too fast, and not too slow either. It's harder than it sounds.
Funny - Scott didn't want to drop his blob of glass, and it kept slipping! So he called to Cynthia, 'Okay, I'm done now!' and she replied with something like 'Keep turning - you're not done yet - gives my wrists a break!'