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by no_news_is 1084 days ago
Answer in your Wikipedia link:

'At the time of its use, the sodium process yielded cleaner results than did bluescreen, which was subject to noticeable color spill (a blue tint around the edges of the matte). The increased accuracy allowed for the compositing of materials with finer detail, such as hair or Mary Poppins' veiled hat. It was also useful that the "sodium yellow" light (and its removal via the matte) had a negligible effect on human skin tones.[2] As the bluescreen process improved, the sodium vapor process was abandoned, its screen and lamps monopolizing huge studios and incurring a higher cost.'