Salutations everybody,
Since materials are on topic i'll use this opportunity to illustrate my final version:
Starting with the left (bowl) side this is a screen preventing vegetal particules from making contact with my heat collector assembly, installed inside the top sphere. Next it's a piece of "shielding-deflector" glass which a metallic (aluminium) support holds in place, though i'd have prefered heat refractory material for this.
Lets mention all of my ceramic filters suffered premature degradation, as a result of mechanical erosion caused during previous/successive moddings; have a look at the middle disc's left side, for example: this part needs to be encased by tripod support (separating the two rocks) or it just wouldn't fit anymore... At least i know it works great as is for me.
The view below shows the bowl-side of my sphere with no screen on:
No (glass) shielding-deflector installed neither... Now that's inside:
More exactly, this is without a front puck and double-ring retainer.
...
No doubt the material's nature is an important variable but i've come to think that maybe the VG pipe concept should try to evolve past simple cylindrical shapes...
E. G. What if VG pucks were non-linear in profile? What if those also came in different densities?... Etc.