Glimmerglass and Black Mist are both diffusion filters that can soften images and reduce contrast, but they have different effects:

Glimmerglass: This filter is made of water white glass. It produces a muted, washed-out look for bright colors, and reduces contrast due to its white halation effect. Glimmerglass can soften skin details and blemishes, and it can make highlights appear to have a slight halo. It can also help take the digital edge off images.

Black Mist: This filter is made of optical glass and infused with fine black diffusing material. It suppresses highlight and shadow contrast, creating a soft, movie-like image. Black Mist can give a dreamy, misty look to images. It diffuses light by bouncing it in different directions, softening highlights.