Transparent Gradient in Illustrator

I recently completed some vector illustrations for an up-coming project. Upon review, a friend asked me how I made transparent gradients in Illustrator. Now compared to Photoshop which has opacity is built, this may seem quite difficult to achieve in Illustrator... but using these four steps make it easy.

Step 1.
Create a solid filled object.


Step 2.
Copy and paste the object in front (Control/Cmd + C, then Control/Cmd + F).


Step 3.
Select the solid object on top and make it a gradient from the gradient palette. (Window > Gradient)


Step 4.
Select both objects, now go to your transparency palette. (Window > Transparency)
Open the fly-out menu and click Make Opacity Mask.
Voilà!