How2 Transparency .

I started of by creating a circle which I filled in with blue.


I then duplicated the selection and filled it with a gradient fill.


I selected the two and in the Transparency options I selected
Make "Opacity Mask".

You might want to change the gradient a bit till you are happy
with how it looks. I then duplicated the circle and using the knife
tool I cut it in half. I removed the outline and filled it with black.


I then did the same thing on the half circle as I did on the full circle.


This how it looks like at the moment.


I then duplicated the whole circle again which I removed the "Opacity Mask"
and the outline. I used the knife tool again. I removed the bit I did not want.
The bit I kept was filled with white. I made the white part about 70% transparent.


And this is the finished Example