And yonder soft phial, the exquisite blue, (15)
This is about a scientific instrument, a vial ("phial"), but mostly we just think it's a really cool line. What a great use of the word "soft." It's a classic poetry moment—the thing she's talking about probably isn't really soft, but it gives us a really clear sense of the effect it has on people. We imagine a soothing, ocean blue liquid, almost glowing in the bottle, hypnotizing the speaker with its beauty.
But brush this dust off me, lest horror it brings (47)
Again, we loop back to the dirtiness, the "horror" of the laboratory. It's a place for ugly secret work, far away from the other location we hear about, the glittering fantasy world of the court, "the King's." If anyone at the court saw her dancing with the dust and grime of the laboratory on her, they'd be horrified. Again, this underlines the generally negative role that science and laboratory work plays in this poem.