You don't actually need a pastry bag to pipe these, but it sure makes things handy. This mixture is too thick to pipe from a plastic bag (the usual go-to pastry bag alternative) so make your own with a triangle of parchment paper instead. Here's a great video on how to do just that.
'cake decorating' on Serious Eats
Gum paste is a sugar dough from the same family as rolled fondant that is used to create brittle sculptures for decorating cakes. It's made from confectioner's sugar, gelatin, Gum Tragacanth (or Gum Tex), liquid glucose, and water. Unlike fondant, gum paste stretches very thin and dries without cracking, which makes it great for creating dramatic, delicate flower petals. It's brittle when hardened, which also makes it useful for decorators, because there is no worry that flowers will melt or bend once they have set.
If you're into making dramatic decorations for cakes out of gum paste, you may want to consider making your own. This recipe requires a few special ingredients that are sold in specialty cake stores, as well as on the Internet.
Decorating cakes the way the pros do takes years of dedication and practice, but knowing a few cool tricks can definitely make the difference between a boring cake and a cake that looks elegant and special. With just a basic set of metal piping tips, there are many impressive designs that you can create to jazz up a cake.
Now that it's become de rigueur to cover and decorate celebration cakes with fondant, the flexible sugar dough that's become exceedingly popular thanks to cake TV shows, Swiss buttercream has become an afterthought. For me, a cook who believes that it's never worth it to sacrifice flavor for appearance, the demise of buttercream cakes is a travesty.
This recipe is extremely versatile and can be used with any flavored extracts. Or, if you prefer to make a natural vanilla bean buttercream, use the seeds scraped from the inside of a vanilla bean. If your flavoring does not impart color, this recipe is great for adding color too. I recommend gel color instead of liquid food coloring, because it contains less liquid and you don't need much to get the results you want.