Isopropal alcohol comes in
Isopropal alcohol comes in different concentrations – typically 70% and 91%. Use the 91% (most pharmacies carry it – and it doesn’t cost a lot more). The non-alchohol portion can contain oils that don’t help.
As Richard suggests, buff your glass clean as a last step. Use a clean, cotton rag. Make sure it wasn’t dried using dryer sheets – they leave residue in the fabric that transfers to the glass.
Helios Kiln Glass Studio