After about one day I usually end up with my black icing bleeding and looking purple. Is there a way to keep this from happening? I have somebody that wants me to do black piping on white buttercream for their wedding cake. I really don't want it bleeding.
I've never had a problem with icing bleeding. (I honestly didn't knwo what it meant until I found CC and read about it.)
I use a very good crusting icing. I apply the black icing only when the base white icing has crusted. I never refrigerate my cakes.
Bleeding happens when moisture is available on the white icing to attract and draw the moisture from the black icing. You may have heard the phrase about water will flow thru the path of least resistence. Moist icing has no resistence..... crusted icing is like a brick wall that prevents penetration.
Refrigerating a cake can cause condensation, which is moisture, which will draw the color out.
This cake used chocolate icing ... no bleeding: http://cakecentral.com/gallery/1341699
Here's one in black icing: http://cakecentral.com/gallery/1300981
The fact that I could "flick off" the white scrolls tells you about how well the crusting works.