Add dark rum, white rum, blackstrap (or aged) rum, fresh lime juice, fresh orange juice, orgeat, falernum (or gomme), demerara syrup, and 2 dashes of Angostura bitters to a cocktail shaker.

Add ice and shake vigorously

Fill the shaker with ice and shake hard for 12–15 seconds until the outside of the shaker is frosty and well chilled.

Glass & Presentation

Prepare serving glass

In a large tiki or Collins-style glass, add a large ice cube or sphere in the center (to resemble the pool centerpiece). Surround the large cube with about 1 cup of crushed or cracked ice to create a 'pool' bed.

Strain over ice

Double-strain the shaken cocktail over the prepared large ice cube and cracked ice so the drink fills the glass and the surface remains relatively smooth around the centerpiece.

Eclipse & Float

Create the 'eclipse' float

If using activated charcoal syrup, carefully drizzle 0.25 oz over the center of the drink so it sits as a dark patch near the large ice cube, creating an 'eclipse' appearance. Alternatively, float 0.25 oz overproof rum on the very top by pouring slowly over the back of a spoon for a glinting dark ring around the cube.

Garnish & Finish

Garnish with a lime wheel or twist placed on the rim or floated next to the large ice centerpiece and tuck a mint sprig into the cracked ice at the glass edge. Optionally, grate a small pinch of nutmeg or cinnamon over the mint for aroma.

Serve with a short straw positioned to one side of the centerpiece so the drinker can sip around the 'pool' and enjoy the layered flavors.