MAC Waveline is a very cool-toned, very dark blue with a pearl finish. It is a discontinued eyeliner that retails for $16.00 and contains 0.1 oz.
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MAC Waveline Fluidline ($15.00 for 0.10 oz.) is a permanent product (and has been for awhile) that is getting repromoted in the new Love & Water Collection. MAC describes this shade as a "navy blue with low level gold pearl." It's a rich navy blue with just a touch of purple--it's barely there but with the right combination of colors could be pulled out. It has good opacity in a single pass and is easily built up in color. MAC Prussian is similar, though perhaps a little more noticebly purple.
Looking for something similar or to see what you have in your stash? Here are some of the top dupes for this product!
Ultra-smooth, Fluidline's gel formula provides the precision of a liquid liner with a silkier, softer finish. Goes on “foolproof” with a brush in an easy dip-and-stroke action. Long-wearing. Smudge-proof. Lines up in a rich array of colours and finishes. Brush sold separately.