I am supposed to do a couple of cakes and would like to try and use royal icing but I am worried that the customer won't be able to cut through the cake to serve and eat it.  Does it just break apart and fall off when cut through?  Or are cake that have royal icing decorations made just for that....decoration, not to be eaten...thanks...

AIt is a number of years since I have used RI. If you are covering the cake in RI then you need to add glycerine to themix to keep it soft. It will set harder than gumpaste but can still be cut with a knife.

I assume that it will be fruit cake. The marzipan should be about 3mm thick and will need to dry out for about a week before you apply the RI. The RI will need to be about 3mm thick too. If you are piping with RI then it depends on the level of detail you pipe and how much "over piping" you do. But generally the piping cracks as you you cut it. Don't forget to allow your RI to rest for 24hours before you use it. This is to get rid of the air bubbles. If you miss this step when you pipe it will be difficult to pipe a continuous line. RI is totally different skills to using gumpaste. If you have not used it before I recommend this book

The international school of ********** book 2. Isbn 978-1853917530

RI takes a lot of practice and a steady hand but does look beautiful. Don't try to skip the drying and setting processes.