Which seems to show that you use the pencil graphite as an electrode and spark i... | Hacker News

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djmips on Nov 25, 2022 | parent | context | favorite | on: “You don't have a voltmeter. Do you have a potato?...

Which seems to show that you use the pencil graphite as an electrode and spark it to ground. The 'fatness' of the spark determines the polarity.

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