Piping chocolate - first - are you sure? Piping chocolate is a pain, and let me tell you why...

Firstly, getting and keeping it at the right temperature. The chocolate has to be warm, so you can't fill three piping bags with different shades of chocolate and work with them really, as they'll cool down. Now if you keep them warm some how then you hit problem two.

Secondly - they leak. Chocolate is slightly too runny to pipe, so it continually dribbles from the end of the piping bag. If you did fill three piping bags up at the beginning, and keep them warm, you'd find that by the time you got to use the 3rd bag, half of it would have leaked out (and keeping them upside down is really easier said than done)

Thirdly, because of this continuous leaking, being accurate with your piping is very tricky. You have to confidently flow from one thing to the next, as the continually dribbling chocolate won't let you easily leave gaps.

Fourthly, you really need to use greaseproof paper piping bags.. if you use fabric piping bags it sweats out and you hands get really slimy. If you use plastic bags then the warm chocolate makes them soft and bulgy and liable to split.

Fifthly Colouring chocolate is hard - you can't use too much or your lovely liquid chocolate turns into a fudgy mess. Pale pastels are about all you'll be able to get away with

Sixthly, once you have managed to make your gorgeous panel, shape, or whatever you have to get it onto the cake, without your nice warm fingers leaving prints all over the beautiful glossy finish.... cold hands, rubber gloves, these things help but it's still a pain. (better to try and apply it to the cake straight from its backing if possible.. kinda like putting on a sticking plaster without touching the back)

On the bright side, you can get a lovely, glossy finish with some beautiful marbling effects if you dribble the chocolate onto a silicone mat or other shiny surface. If you're very careful you can place the mat over slight curves to shape it, and using a sharp knife you can take lovely marble coils from the top of the sheet (best for the chocolate to be at room temperature for this - too cold and it just chips). It makes a fantastic coating on a chocolate cake too

Plus, if something goes wrong, you can always melt it down and try again!