This New Years I had a bottle of Chambord, the raspberry liquer, and I sipped it through heavy cream. The cream is dribbled over the back of a spoon, to pool on top of the liquer in a seperate layer.
I have heard that different liquers themselves can be layered like this, sometimes even in threee layers, but have so far not found lists of the specific gravities of them, to know which are lighter and which heavier.
There are some disagreements between the two sources, for example Crème de Banana is listed as 1.18 at one site and 1.14 at the other.
This is probably due to brand variation. Different amounts of sugar and different amounts of ethanol will give you different densities. Thus the tables can be helpful as a buying guide, but the final proof of the pudding is in putting a drink together with your own booze and seeing what sinks, and what floats.
Here’s a good guide to pousse cafés. Thirty-five years ago in San Francisco at a Fisherman’s Wharf restaurant with a snooty faux-French waiter, I watched in delight as he dropped the haughty pose and crouched down eye-level with the bar to help the barman check that the pousse-cafés I had ordered for my fiancé and I were going well. They did a superb job, served the five-layer (Or was it six? Lots of layers, anyway.) drink with a flourish, and a big smile.
It may just have been my imagination, but he may have been tired of whiny tourists, and a chance to show off a fancy drink in the middle of what was a quiet afternoon might have tickled him somewhat.