Eevee Transparency gradient started blender a month ago.

I'm trying to combine nodes to create a specific skin effect on BLENDER 2.8, Eevee. 

The one you would see on the chin of a breathing frog. A skin really tensed, with a gradient of transparency opaque at the bottom, nearly see through at the top of the "sphere".



I tried all the advices to do glass, plastic or I don't know. None of them where satisfying and had any real control over the area of transparency, nor the gradient I'm looking for. I Tried to combine it with a fresnel, I was close but no gradient, even with a color ramp.

I found out this awesome video solving the problem throught texture painting:

https://www.youtube.com/watch?v=O5PpEkv1ls4 

It works for me. The problem is that I'm not using any texture, only nodes. I don't know how to paint on it.

Do I need to first finish my mesh, somehow extract the "node texture" from it, re-apply it, and then paint it with transparency?

Any suggestions?
Thanks a lot for your time.

Arthur
Here is a node setup to achieve the transparent gradient sphere effect:




I'm using a Mapping node to control the direction of the gradient, Gradient Texture node for the gradient itself, and a ColorRamp node to control the transition. For the transparent part of the object, I'm using a glass shader with IOR very close to 1 (or it will look like real glass), and 0.6 roughness to make the object behind appear more blurry.

And make sure you enable screen space refraction in both render and material settings, or the transparency won't render correctly.

I don't know why you are trying to avoid using textures. While this procedural setup works well on a sphere, I don't think it will work if you are going to apply it to something more complex (like a frog model). Since it's using a simple linear gradient, it's very hard to make it fit perfectly on the frog's chin. I would recommend using texture painting if you really want to do that.