I’ve been very pleased with
I’ve been very pleased with the “Ti Pen”.
It is a titanium tipped pen that marks glass permanently. It actually leaves a titanium line on your glass that can withstand a full fuse without being “erased”.
The mark is very subtle (shows up better on darker glass). The pen is popular among lampworkers who need to make very small, subtle marks.
You can get it here:
Helios Kiln Glass Studio