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anothersilentone 7 points ago +7 / -0

Ink is a mixture of dyes, solvent, and other media. Each individual chemical in the mixture will have a unique "signature", or spectrum. There are a number of spectroscopic methods that can be used to identify chemicals and mixtures of chemicals.

If the ink used to fill in the bubbles on all the ballots all have the exact same spectrum, then they all had to be done with the exact same pen.

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JustInTime2_ 2 points ago +2 / -0

Thanks for the explanation Pede.