Hi, I had some trouble with a royal icing plaque I made last weekend. It was royal icing, tinted with wilton colors. I let it dry for 24 hours, then piped on top of it with some cakemate white writing frosting/gel stuff in a tube, I got it at Walmart. I've never used it before. But I did try it out on a 2nd plaque the night before, which worked fine.
My problem is that the plaque began to have grease spots, growing as time went by. The spots were not isolated to where the white writing was, so I don't believe that was the cause. Could it have been from the all crisco frosting underneath it? It seems strange to me that would cause it, since people use royal icing for wedding cake flowers. But I know that grease will break it down when mixing it. Am I just dumb? Should I have known this?
How would I prevent it in the future? Thanks Tammie
Judging from the situation you described, and my experience with the Royal Icing on a buttercream cake, it's not only when you are mixing the icing. When royal comes into contact with buttercream, it will break down....even after the royal icing has dried.
Maybe someone else who reads this could have a solution to this problem.
Anyway, hope this helps, and good luck! 
Grease of any kind will break down royal icing. That's probably why you got grease spots. Next time you can use more royal to decorate or try doing a gumpaste or fondant plaque instead. 
)
At the risk of confusing everyone, my experience is a bit different. My royal icing flowers have never broken down on a buttercream cake, and I have been decorating for over 20 years. I use the royal icing egg white recipe. However, I have never decorated a royal icing plaque with buttercream. If I make a royal icing plaque, place card, etc. I always write or decorate with royal icing.
Go ahead and make your plaques as you do, but place sugar cubes under it so that the royal doesn't come in contact with the buttercream. Just push the cubes halfway in and you can even pipe tiny dits of royal on the cubes if you're aftaid of slipping, and it'll be fine!
Hi...I am a novice, and had planned on trying to make Royal icing flowers ahead of time to place on a cake that will be iced with buttercream. Can I not do this???? I just assumed it was done all of the time. Told you......I'm a novice. I was going to make them ahead, so the actual decorating would go quicker. Could someone please let me know if I can do this? Thank you so much.
On my cookies I use RBC with RI and have never had a problem....
When I made my Wilton Course 2 final cake it was RI flowers on butter cream. I kept my cake for 2 weeks in total before it went in the green bin.
After the first couple of days I noticed that the RI flowers started to change color a bit and got softer. It was like the royal icing was absorbing the grease from the buttercream. After 2 weeks it was really ready for the garbage. Overall all though I think it held up really well.
I know - why would I keep a cake for 2 weeks?? I was so proud of it I could't bear to cut it. I would look at it every day. I know I am pathetic 
punkinpie...you are NOT pathetic! You were PROUD, and I think that's wonderful. I have not taken the course, but intend to do so. I made teddy bear cakes years and years ago, and I was so proud, too. If I ever make a cake with flowers, etc., I may just put it up in the attic with the rest of my "junk" I can't bear to part with! LOL JUST KIDDING!!! But, I will keep it for a couple of weeks and look at it every chance I get! LOL
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