Hi all, sorry for all the optics-related questions lately

I am attempting to create a shader that looks similar to “gummy worm” candies, where the object is transparent at the thin areas and colored more and more as the object gets thicker, like in this clip by Trashbin [www.instagram.com]

I've been experimenting with the At Distance settings for transmission color (red) in the Principled Shader. My intuition was that because the distance across a sphere is a lot thicker than anywhere else on the sphere, using At Distance with a relatively high value would make it so that the center of the sphere would be the most red and would get gradually more and more desaturated and eventually transparent towards the edge. However I have only been able to change the saturation for the entire sphere with At Distance.

Am I misunderstanding how Mantra/Principled Shader handles transparent objects? Or do I misunderstand optics altogether and my initial hunch of having to use SSS correct?

Why are you sorry? If you think posting questions is bad, you should stop doing it and if it's not, you should stop being sorry
Before getting a more detailed answer, my tip to you when experimenting shading is to use detailed geometry. It's much easier to read tweaking of the settings as it gives you a closer look to real life objects.
Use the test geometry. (Tab menu> Test…)

edit: looking at that link it seems that's a matter of transparency roughness; I don't have H in front of me to tell you the exact name

Ah well. I feel a bit guilty because I've been cluttering up the forums with newbie questions without being able to contribute to discussion in return! It's silly but that's how I roll sometimes

Alright, I'll try more experiments with the Rubber Toy this time, and return with results later.
Wouldn't transparency roughness be SSS?

I lied! I had to use Tommy because the Rubber Toy's fins were exhibiting weird behavior due to them being “separate”
from the rest of the geometry

Aw phooey, you were right

Some disturbing results but nonetheless exactly what I wanted. Now only to figure out why he's got those stripy reflections…

A sphere is a bad example for visualizing attenuation distance, due to the degree to which rays are bent. A ray entering a sphere tends to travel the same distance regardless of which angle it enters. So it is correct for it to look uniformly saturated.

As to why your tommy has odd reflections, I cannot say. I don't see that when I make a simple scene with a point light and env dome and white grid. If you post a scene file, maybe someone can advise where you erred.

georgina
Ah well. I feel a bit guilty because I've been cluttering up the forums with newbie questions without being able to contribute to discussion in return!

Nobody's keeping tabs, so relax
Pics are good, but as jsmack said, if you pair them with scene files it's even better.