I have a question for my final project flowers & cake design Wilton class this week. I am confused. I understand that the slightest bit of grease/oil will mess up RI but a lot of the cake designs in the book imply/state to use buttercream icing. Won't this cause my flowers to become ruined? TIA!

Once your royal frosting decorations have dried they will be fine. What you need to be careful about is when you are making royal frosting. You need to make sure that all items used when making royal are oil and grease free even your cake decorating tips and couplers. I soak my couplers in dish soap and vinegar and clean them well. I don't use reusable cake decorating bags if I have used them for butter cream as it is almost impossible to get them 100 percent oil free. Enjoy your last class.

I took this course in June and yes, as the PP mentioned, you have to worry about the grease when making and mixing your royal. After it's dry you're good to go. I know our instructor told us to stick everything in the dishwasher on hot because the heat helps to eliminate the grease. That's what I've done and I haven't had a problem when making my royal icing. Make sure to give your flowers plenty of air time to dry up nicely, especially if you live in a hot and humid state like I do. Good luck!

Yes, grease-free utensils while you're making it, but it doesn't have to be a grease-free surface that you pipe it directly onto, nor completely dried to stop it from breaking down. (moisture is the culprit.)

There's a similar thread from a few days ago that discusses what causes royal icing to break down titled "Deciding between fondant, icing, gumpaste, and buttercream". I'll paste what I wrote below...
Here's the entire thread: http://cakecentral.com/cake-decorating-ftopict-696720-royal.html+icing

...you can apparently make royal and pipe it directly onto Crisco greased forms and pipe into cooking-sprayed foil-lined lily nails!)

If you'd like to read what others have experienced, TexasSugar says that it's caused by moisture in this thread "question about royal icing":
http://cakecentral.com/cake-de.....html+icing

and here "Royal icing decorations":
http://cakecentral.com/cake-de.....html+icing

my favorite "will piping gel break down royal icing":
http://cakecentral.com/cake-de.....html+icing

another favorite, "Royal Icing Lilies, Cooking Spray...":
http://cakecentral.com/cake-de.....html+icing

CWR, thanks for sharing those links.

I've always wondered if Royal couldn't touch buttercream why would anyone ever make and use it? Wilton courses have been going on for over 35 years. I've actually been teaching them for over 6 years and have yet to have a student come back in and say that all their flowers melted on the cakes.

I would avoid putting royal icing decorations in the fridge or on a cold cake because the condensation can cause problems. I also wouldn't put the cake with royal icing decorations in an air tight container, thus allowing the royal decorations to absorb moisture.

But other than that you should be fine.

I also do not go to extremes when it comes to making the icing. I don't have a dishwasher so I just wash everything in hot soapy water, that's it. I've heard of people that wipe everything down with vinager and even have a seperate set of tips they use for royal. I've never had to do that, nor have I had any problems making or using it.