Online

What the heck is a "glass stack" electric field generator?  They were once available for purchase or used in "industry".

We can't find them "online" now.  They may or may not have "disappeared" before the "internet" was a thing.

How did they work?

That may or may not be answered backward with details of their construction or operation:

• One or more alternating layers of "glass" (or non-conductive material) and "something" else (more or less conductive material).
• One or more sources of "resonance" or "vibration".
• "Shaken" or "stirred".

What did they do?

That's a complete "mystery".