Former forensics guy here.
While I've always questioned the watermarks story, there are a lot of pen inks that fluoresce or reflect UV light differently than printer ink or toner.
It's one technique to figure out what bubbles are printed vs. filled by hand, if marks were made by different pens on the same ballot, things like that. A quick UV pass looking for bright visual anomalies is a pretty effective triage technique, even if there are no watermarks embedded in the paper.
I have a vague memory of Dr Steve Pieczenik speaking about the watermarks shortly after the election. His statement was that the watermarks on the legitimate ballots were made using a radioactive ink, and were thereby easily identified. It sounded strange at the time, which is the reason it stuck in my mind. But after looking up the definition of fluorescence just now, his statement makes more sense:
fluo·res·cence: the visible or invisible radiation emitted by certain substances as a result of incident radiation of a shorter wavelength such as X-rays or ultraviolet light.
Former forensics guy here. While I've always questioned the watermarks story, there are a lot of pen inks that fluoresce or reflect UV light differently than printer ink or toner.
It's one technique to figure out what bubbles are printed vs. filled by hand, if marks were made by different pens on the same ballot, things like that. A quick UV pass looking for bright visual anomalies is a pretty effective triage technique, even if there are no watermarks embedded in the paper.
I have a vague memory of Dr Steve Pieczenik speaking about the watermarks shortly after the election. His statement was that the watermarks on the legitimate ballots were made using a radioactive ink, and were thereby easily identified. It sounded strange at the time, which is the reason it stuck in my mind. But after looking up the definition of fluorescence just now, his statement makes more sense:
fluo·res·cence: the visible or invisible radiation emitted by certain substances as a result of incident radiation of a shorter wavelength such as X-rays or ultraviolet light.
I think you nailed it.