Tracer’s Black
You can get beautiful, fine black lines with tracing black mixed with clove oil. This is the same stuff that traditional glass painters have used for hundreds of years.
Here’s an example (part of something I’m currently working on). The writing was done with a fine point calligraphy pen. Don’t bother trying to read it — it isn’t real words (but could be). 
Paul
FusedGlass.Org
Helios Kiln Glass Studio
PaulTarlow.com
