I am trying to render an object that has opaque base and gradually becomes clear/translucent at the top in Blender cycles.
Please see the attached image (which was not made with blender).
All you need to do is use a Gradient Texture (see how to create it procedurally here: How to create a gradient texture?) as a mask for the transition between two materials.
All you need are a two shaders the opaque (Diffuse node), and then the transparent (Glass node), then a way to mix them together.
Here I'm using the Z axis of generated coordinates. Generated coordinates always go from zero to one along each axis of the object.
The color ramp node is to fine tune the mixing between the two shaders.
the transition seems to be based on the height of the shading point and for that we use the Z component from the Position output in the Geometry node and using division ( math ) node we can normalize the height , then we use this as an input for the mix shader to create the transition between a glass material and a diffuse material: