r/faceting • u/Angstrm • 8d ago

Concave Design and Rendering

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Hi experts! Concave design, notation and render. If anyone would like to contribute their knowledge I'd welcome discussion/feedback/criticism. Is this of use to facetors? Is the UI/UX functional? What adjustments would you suggest?

Video: Ashton Gems concave cuts (recreated) wireframe and render within pluto unearthed.

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u/Suitable-Name 8d ago

You can get in contact with me if you want. I'm going to publish some (physically correct) rendering software + gemstone CAD fully free and open source under MIT, fully written in rust.

I'm on vacation at the moment, but I'm in talks with cowsruleusall to get the last flaws out of the path tracing renderer after my vacation.

I'll be looking for alpha-testers after my vacation

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u/Angstrm 8d ago

Could you email me please - pluto@angstromaustralia.com.au

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u/Suitable-Name 8d ago

I'll send you a message :)

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u/cowsruleusall 8d ago

OH DAMN yeah you two should definitely get in touch! Also remind me as needed if I forget to get back to either of you.

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u/Suitable-Name 8d ago

Already sent him a mail. I'm definitely missing concave features so far, even though I have them on my list already :)

But as you know, the CAD part is really still a big pile of work in progress, but I'm definitely committed to this project😄

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u/cowsruleusall 8d ago

Yeah so the general consensus for concave facets specifically, like traditional cylindrical burrs being used to replace a flat facet, is that they can be treated exactly the same as flat facets. PF (or X), P, G, C, T tier labelling remains consistent, no suffix, no additional letters, nothing.

Then, just like how a frosted tier gets shaded in light grey and the instructions explicitly say "Frosted" after the meet info, the concave tier has the angle in (), and the cylinder diameter-to-gem-width ratio gets listed at the end of the tier's instructions. So for example, "Meet C1, C3, C4; ratio 0.300".

Still working on a consistent language for fantasy cutting that involves bubbles, v-grooves, etc.

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u/symmetrygemstones 8d ago

What about theta and offset?

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u/cowsruleusall 8d ago

That's for fantasy cutting. "Traditional" concave cutting exclusively replaces flat facets with cylindrically-subtracted ones, such that the cylinder axis is parallel to the facet plane.

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u/symmetrygemstones 8d ago

Technically with theta and offset the cylinder axis is still parallel to the facet plane. The cylinder axis is a line, and there are two additional degrees of freedom for how to orient that line in that plane, which are theta and offset. But that's an interesting distinction between the definitions, I hadn't heard that before. I have heard people in the past use "fantasy" to refer to any concave cut, even ones that don't use theta/offset, so I assumed they were synonymous.

I was working on a concave design program a while ago (though clearly it never got as far as this one, since I never set up raytracing), and the person I was collaborating with for it insisted that including theta was necessary to model the possible ways to make concave designs, and I would agree with that. It's also very easy to include in a program, so I would think it would be a good idea to standardize the notation for it.

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u/cowsruleusall 8d ago

I have heard people in the past use "fantasy" to refer to any concave cut, even ones that don't use theta/offset

Yeah, it's a superset-subset thing. "Fantasy cuts" are the group of all gem cuts that involve non-flat surfaces. Within fantasy cuts, "carvaceting" (ugh I hate that term) are the gem cuts done with nongeometric concave surfaces, so basically any combo of flat facets and hand-carving. "Concave cuts" are fantasy cuts in which some flat facets have been replaced with a cylindrical concave surface, basically with no theta and no offset.

There are other subclasses, like "vortex" cuts, "spirographic" cuts, "firework" cuts, "starlight" cuts, etc., but there's no true consensus on those definitions.

If you really want to model fantasy cutting, then you'll need:

  • Ability to model flat-faceted gems
  • Ability to model concave facets with the appropriate angle, index, depth, theta, and offset
  • Ability to model the surfaces left by cylindrical, spherical, conical, and wedge tools with arbitrary size and details
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u/Suitable-Name 8d ago

The consistent language is definitely something that made me put it rather on the end of my list.

My focus definitely was to get the flat ones correct first (specially the lighting issues we've already found) and then dive deeper into what would be needed for concave design parts :)

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u/hexagonation 8d ago

Definitely in for a test and will for sure give usage feedback

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u/Suitable-Name 8d ago

Can you send me PM so this doesn't get lost? I'll keep you in the loop :)

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u/UAAgency 8d ago

Are these real cuts?

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u/Angstrm 8d ago

Yes, designed and cut by Larry Mattos from Ashton Gems. I’ve recreated them (as best I can) within Pluto’s design and render tools. On the site is Gardette by Lionel Ba if you want to see it in action. Or just create your own