A Black Velvet is made by filling a vessel, traditionally a tall champagne flute, halfway with sparkling wine and floating the chilled stout beer on top of the wine. The differing densities of the liquids cause them to remain largely in separate layers (as in a pousse-café). The effect is best achieved by pouring over a spoon turned upside down over the top of the glass so that the liquid runs gently down the sides rather than splashing into the lower layer and mixing with it.
有道理。