I hadn't looked at this project in awhile, and discovered that way back when I'd ordered some inverters and XOR gates! Free parts, just sitting there.
So I built a quick circuit with one of the hex inverters (CD4049) to drive the glass:
The formula for frequency is determined by R1 and C1 is F = 1 / (1.39xRxC) ... I tried with a 47k resistor and a 330k. In both cases, the glass appears dark.
What I want though, is for the glass to be able to dim. The correct driving wave form should look like this, but in order to vary the brightness/ dimming, needs a PWM signal.