Bonded metal laminations and insulated epoxy coating. Hmm. . . Sounds like your company makes transformers. Have you looked into the making of transformers. The process used for making these is very close to what you're describing. Look into it. It might help explain what you're looking to understand. Hope this helped.
Some megaohmmeters can supply hundreds, even thousands of volts to read giga-Ohms with any kind of resolution.
This "Model 1300 Gage Insulation Tester" measures up to 20GΩ with only 15v, therefore much improved engineering was done for signal fidelity.