Thank you all!
@denny
I get my Rattan from Germany
@Josh
It is one little piece and I made the curves with the heatgun
@KenH
Yes, working with Rattan is not to compare with woodworking, Rattan is very light and has very long fibres.
@NTD
I used the outside of the rattan for the back of the bow. Torges is right in using the outside of the Rattan for the belly, because it is harder and better under compression. But I like the looks more the way i did it.
Matthias