If you want to create the gradient from bottom to top of the object without using texture UVW mapping then the receipe would be the following:
1) create the uvwProjection node with XYZ projection method
2) create Pattern node with linearY pattern type and connect uvwProjection to Pattern.inputUVW. This way you will get greyscale gradient.
3) create Ramp node as you did and connect the former node output to it's input map.

As for glass material you may attach the resulting node to Transmission Color or Absorption Color. Also you may variate the absorption distance with a texture