The dark part of the mark is the unlit side of the moon; the light part is what was shining on the water. Five bottlings follow the waxing half of the cycle: New Moon (charged under starlight, zero moon-hours — we say so), Waxing Crescent, First Quarter, Waxing Sparkling under the gibbous, and Full Moon.
A note the evening before each charge, and first access to limited phases.