I'm gonna go with "never" because seriously, unless you're spilling it everywhere, it lasts until it dries out, usually halfway to two-thirds down the bottle. You never "run out."
That said, I have just gone through an entire bottle of Essie Blanc in the last 6 months. White is a staple colour for me. I use it in every other manicure, from french tips to skulls to backgrounds for water-marbling. Blanc was fine, but I was looking for something new. Something like....
Alpine Snow! This is the white most used in the nail art world (or at least the blogs I read), and I think that honestly, the formula is not noticeably different from Essie. White is always streaky, but what makes Alpine Snow better for me is the brush. OPI brushes are wide and easy to maneuver, and that makes them top-notch.
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