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The purple glasses they wear are didymium. Photographers use a less intense version of that material as a "red enhancer filter." The spectra of the glasses ( https://www.colby.edu/chemistry/CH332/laboratory/didym-spec.... ) have a very low transmission from 572 nm to 585 nm. That's a yellowish color. The sodium vapor lights (those yellow street lights) are 589 nm. For photography, if you block the yellow out of a muddy brownish-red you get a more vibrant red. For glass blowers, the yellow flame around the glass is the sodium in the material ( https://en.wikipedia.org/wiki/Flame_test - look at the sodium line). By blocking that yellow light, a glass blower is able to more clearly see through the flame to glass.
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For people who are interested an intersection of STEM and art... there is a demand for scientific glassblowers. ( https://www.theverge.com/2020/3/10/21172370/scientific-glass... - the woman in the article is https://www.phoenixmag.com/2017/10/01/christine-roeger/ who is a third generation glass blower - my father learned to fix a few items in the chemistry lab from her grandfather).
> She’s one of about 650 scientific glassblowers in the U.S., one of only a dozen or so women in the field, and one of even fewer third-generation scientific glassblowers. Running Arizona State University’s Glassblowing Facility as a one-woman operation, she’s carrying on a long but unheralded tradition that goes back to the makers of Galileo’s thermometer and Thomas Edison’s light bulb.