I am making a cake for a birthday tomorrow - it's covered in Buttercream and will be decorated with a floodworked royal icing Pooh Bear (I think you call it colourflow?). I've never attempted either before, but I realise I should probably put the Pooh Bear on as close to pick up time as possible?
How long can the royal icing last before it starts to break down into the BC? Of course its red and black and yellow, on white BC :S

If your flooded image is quite dry and the buttercream has crusted somewhat (assuming that you're using a crusting buttercream, of course), it probably won't start to bleed into the white background for several days. At least that's been my experience.

It won't start softening or melting the instant it hits the cake. If possible you can put it on last minute, but I've done them the night before with no problems. Just don't put the cake in the fridge or close it up in a air tight container. Moisture is a bigger issue than the actual grease in the buttercream after the piece has dried.

I've piped royal icing directly on a fondant cake that was smeared with crisco, no problems with melting, bleeding or anything and I even used black icing on part of it.

Have you tried Kathyf's glaze method. It's wonderful. This is what I do when I need to add a picture on a cake if I'm not using fondant. Instructions for pictures on cakes using my glaze method - Kathyf

Frost your cake and smooth with wax paper as soon as the icing has crusted slightly. You can transfer a design/picture to
the cake using a projector, airbrush or by using a pattern made by poking holes in paper placed over styrofoam with a
corsage pin. Use a tip 1, 2, 3 or 4 to outline the design on the cake. The larger tips are easier to draw with, but with the
smaller ones you can make a more detailed design. As soon as the outline is dry enough so you can touch it without it
sticking, lightly flatten it with your finger. This prevents the glaze or gel from leaking under the outline when you fill it
in.
You can fill it in right away but it is easier to work with if you wait 2 hours or longer. It will also prevent colors from bleeding
together if the outline is dry before filling it in.

I use a glaze made from 2 lbs. powdered sugar, 1 T clear vanilla, 1/2 t. almond flavoring, 1/4 t salt and 3/4 c water. The
amount of water can vary. Mix it to a consistency that works best for you. A good guideline is when a small amount of the
glaze is dropped back into the bowl, it takes 3-6 seconds for it to disappear. The thinner glaze is easier to pipe into the
design, but a thicker glaze is needed if you are using it on a cupcake with a surface that's not level. If your glaze is thin you
need to be careful filling in the design or it will overflow the outlines. It crusts quickly, so complete one area at a time,
working from the outside to the center of each section.

The glaze can be put in a disposable decorating bag with a small hole cut in the end or piped from a parchment cone. I use
disposable bags with a hole the size of a # 1 tip. Close the top of the bag tightly with a rubber band. The glaze can be kept
refrigerated for several weeks or frozen for several months. Parchment is more economical if you only use this method
occasionally. If the glaze is saved it will separate in the bags. Pinch the open end of the bag and knead the bag to re mix it. A
small piece of tape can be placed over the end when storing the bags to prevent the glaze from leaking.

Petal or luster dusts can be mixed with lemon extract and painted onto the glazed areas after they are dry. It takes 2-8 hours
for it to dry enough to be painted on. Smaller areas dry quickly. Larger areas take longer. If you attempt to paint on them
before they are dry the glaze will dent.

Make sure you use good support under your cake when using the glaze. If the cake board bends the glaze surface will
crack.

Sorry so long but it won't let me link the website that the instructions are posted on. Same idea as colorflow but you can cut through the image and have no problems with refrigeration or you image melting.

Thanks everyone

I ended up doing a very last minute fix up this morning. The buttercream wasn't as smooth as I'd hoped, and everything I did seemed to make it worse. I re-covered eeh top in Betty Crocker frosting, and got a smooth surface, but piping freehand was a whole new experience!
I ended up aith a great looking Pooh Bear and some slightly sloped writing.... definately not my finest cake, but it's what the Mama wanted so I had to give it a go.

I look forward to trying the glaze method though- thank you!