OK.  I've searched and read what I can find on the topic here and I've been reading different suggestions, so I don't know what to do!  I have a white fondant wedding cake coming up that has black piping on 2 of the tiers.  I am so much better at piping with buttercream than with royal icing   I don't know why.  I am so worried about the black buttercream piping bleeding onto the white fondant.  I even did a test piece of fondant and put black piping on it.  It seems fine.  Should I be worrying so much?  Has anyone piped with black buttercream on white fondant before?  And if so, do you have any suggestions?  And for those of you who pipe with royal, why is it more difficult for me to pipe with it instead of buttercream?  I don't get it. 

anybody?

Yes, I have.  And I was super worried too but as long as the fondant has been freshly applied and hasn't sat in the fridge over night then been brought into the warmer kitchen air and has started to sweat before you try to apply the royal, you really will be fine.  I don't know what problems you're having but a good trick with royal is to place something under the front edge of the cake - like a 1/2" stack of paper - just so that the cake tilts back ever so slightly while you're working on the side designs.  That way it won't stretch out before it hits the fondant.  Another problem is getting the royal consistency perfect.  Too stiff and your hands shake and hurt.  Too loose and - well, we won't even go there.  Are you having trouble with your tip clogging?  If so, strain the royal through the toe of a new pair of panty hose.  All the best to you.

Thanks so much DeniseNH!  It makes me feel better to hear from someone who has used black BC on fondant and didn't have it bleed!  Maybe my problem with the RI is the consistency.  My lines just don't seem as smooth and tend to be more "squiggly".  Maybe it's my speed and pressure...I just can't seem to do it right.  Practice, practice, practice!  I will try tipping the cake slightly too...

I do feel much more comfortable with the buttercream piping though.  I'm probably going to go that route now that I know it has been done with success!

AI piped the Eiffel tower just recently (3Dmodell) and it took me several attempts to get it right. In the beginning my hands were shaky and I was nervous. The next day and several batches if RI later I felt more comfortable and I worked fast and steady. If I would have to pipe on a wedding cake and wouldn't feel confident yet, i'd practicing the design on a dummy first...

Oh yes!  There has been lots of practice!  I am very comfortable piping it in buttercream.  I do ok with royal icing, just not as nice as the buttercream...I always practice and make sure I am confident when I am doing a cake that customers are paying for!

I've been under a lot of stress lately and misunderstood your question.  I haven't used BC on Fondant but Royal only - I'm so sorry I lead you down the wrong path.  Royal is the way to go because it sets up fast and can be put on thinly.  Yikes, going back into my bat cave now.  So Sorry.  Looks like others have done this successfully but I haven't tried it yet.

No problem, DeniseNH!  We all have those times!  You have been very helpful!  No wrong path!