We here all do/should know about the ubiquitous 'Leyden Jar', as described in...
https://en.wikipedia.org/wiki/Leyden_jarHowever, I just watched an old youtube video with Professor Julius Sumner Miller, where he demonstrated a physical
construction of one, using 2 aluminium cans and a glass jar stacked together. OK, that sounds good... He then charged
one of the 'plates' with high voltage, and demonstrated a strong discharge spark between the 2 metal components. OK.
He then repeated this, but before discharging it, he pulled it all apart, and 'grounded' all the parts, including touching the
metal parts together, before re-assembling it all with the glass jar. He then demonstrated by connecting the 2 metal parts
with a spark,that the 'charge' was still there??!! He has a habit of leaving 'experiments' for people to work out why, by
themselves!... It has me confused. Actually, his whole video is interesting, but the point I mention starts here...
https://youtu.be/4wa8IKMYwK8?t=358