Fading opacity material

[solodesign]

I was trying to have a fading effect both in color and opacity over this glass ball.
So I made a square on Illustrator and applied a grey gradient and exported as a PNG image.
I made several attempts so to find the right fading I was searching for.
Each time i loaded the exported PNG image as opacity map until I was satisfied.
Then I just changed the colors from greyscale to CMYK to have the same fading gradient as the one in the opacity one.
Then I simply loaded it as a diffuse map.
This is the result.
Do you think there could be a better way to do that?
I started from hard shiny plastic material.



Marco