Hi everyone. I was wondering how you decide when to use gum paste over fondant or fondant over buttercream. And when is royal icing most appropriate?

Thank you...

Gum paste is for things that need to dry rock hard, like shoes, flowers on wires, loopy bows. It can be rolled thinner than fondant. It dries faster than fondant, so you've got less time to make whatever you're making before the outside gets too dry to work with and starts cracking.

Fondant stays soft enough to cut and to chew when it's on a cake. You can make figures and bows out of it but it's going to take a long time to dry.

Deciding whether or not to cover your cake with fondant just depends on your preference, your client's preference if the cake is for someone else, the style you're going for, your abilities, etc. When you put fondant on a cake, you still have a layer of buttercream on the cake before the fondant goes on.

Royal icing dries rock hard and doesn't taste like much of anything. It's good for delicate details and piping on top of fondant. You can't put royal icing decorations on top of buttercream because the fat in the buttercream will break down the royal icing.

Great explanation, however, I disagree with this:

When making RI, it needs to be grease-free, but not after it has dried. Buttercream can cause grease stains on RI or cause it to darken as it absorbs some of the grease, but it won't break it down to the point that it would melt ordinarily, unless it's something very thin.

RI is used on BC in many ways.
Take for instance, those "Happy Birthday" letters that are packaged at the grocery store... made to be placed on birthday cakes.
RI drop flowers, tiger lilies, etc.... made to be placed on cakes and surrounded by BC leaves. (It can be used successfully with nearly endless possibilities.)

Royal icing also makes the best "glue" for decorative 3D structures made from pretzels, candy, etc. -- like on gingerbread houses.

When I was first starting out, I made tons of RI flowers, dried them for a week and put them on a buttercream wedding cake the day before I needed it. The next day, the smaller flowers were puddles of goo and the roses had melted about halfway. I was using the standard Wilton buttercream recipe back then. I told my mom, and she said it was the grease that did it. Were we wrong?

Thank you all for your help! Every little thing helps. Hopefully one day I'll get as good as any of the artists in the cake gallery. So far mine are not so impressive.