Hi, Mike!
The leakage current you mention
could be regarded as a resistive
pathway in parallel with the
capacitive pathway through the
glass dielectric. Together, they
may exhibit an RC time constant.
A Wheatstone-like a.c. bridge circuit
may reveal the frequency response.
If we were really lucky, the product
RC might be a convenient size due
to R being relatively large and C being
relatively small (in comparison to
ranges of readily available instruments.)
Then it might help clarify
the mechanism of the process,
if it is reproducible.
Best wishes,
Matthew
