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31 Oct 2024 19:27:20 EDT (-0400)
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From: Thomas de Groot
Subject: Re: Fluorapophyllite-(K)
Date: 29 Oct 2021 11:05:28
Message: <617c0db8$1@news.povray.org>
Op 29-10-2021 om 02:05 schreef Samuel B.:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> Correct. This needs a good knowledge of crystallography indeed. I am a
>> layman on this really...
> 
> It doesn't really take any in-depth knowledge. Just a bit of time reading and
> browsing through images of minerals. (Which might be too time-consuming,
> depending...)
> 
I just browsed through the one (microscopy) crystallography book I still 
have. Principal cleavage plane is indicated as (001), meaning the 
horizontal plane.

>>> And then there are clouds... Similar to fractures, the clouds you see in
>>> minerals are often reflective/refractive gas or liquid pockets, and so they
>>> might not easily be replicated with scattering media. (...)
>>>
>> Inclusions, yes. Scattering media is a poor substitute. There are the
>> little foreign grains that got included, and the fluid inclusions. Those
>> are really interesting!
> 
> Yeah, there are many fascinating inclusions that can occur in minerals. I
> remember seeing a photo of some white crystals occasionally found in obsidian.
> IIRC, they formed in groups of four tetrahedral crystals meeting at their
> corners. Pretty much like the first iteration of a Sierpinski tetrahedron. If I
> come across the image again, I'll post it. (Image search isn't turning up
> anything relevant, and I originally found it in a book.)
> 
>> [Aside] in a very distant past, my wife did a study on fluid inclusions
>> in quartz crystals from Greece. She could, by cooling the crystals in
>> liquid nitrogen and then slow heating, determine the original
>> temperature of the liquid in which the crystal grew. Original pressure
>> was somehow derived from other factors. I forgot. [/Aside]
> 
> Crazy! I haven't a clue how those environmental factors could possibly be sussed
> out. That's hacking, as far as I'm concerned... Physical hacking, not digital,
> which is even cooler. She sounds like an awesome woman :)
> 
Ah! but she is of course! :-) She didn't remain in the Earth science 
world however, and switched to French literature (as she is French 
herself, that was a natural if not the most easy choice here in NL).

>> But, those fluid inclusions are difficult to model. I was thinking about
>> clouds of bubbles in liquid (there are a couple of scene files drifting
>> around in the pov world; I think I have a couple of those somewhere)
>> using a gaussian distribution scheme...
> 
> Inclusions are pretty much the main impediment to making better mineral renders.
> 
> And inclusions take on many forms. Not all exhibit crystalline features when
> viewed with the naked eye (e.g. light reflecting at certain angles only). Some
> do, though. I had (or still have) a Herkimer 'diamond' that apparently has an
> inclusion in the shape if a tiny quartz crystal. The bubble really looks like a
> tiny, doubly-terminated quartz crystal. I'll have to take a photo of that.
> 
>>> Besides the symmetry, another thing I noticed about the crystal libraries in KS
>>> is that the secondary and tertiary faces (modifications) tend to be somewhat
>>> exaggerated. (...)
>>>
>> Yes, I have been wondering about that. Not being an expert, I have been
>> hesitating between the different models proposed.
> 
> Eh, nothing is written in stone. (Haha, except stones.) But there are always
> outliers to these things. Depending on the conditions in which a chemical is
> grown, modifications may become more or less prominent. You never know.
> 
I am going to experiment different paths...

-- 
Thomas


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From: Kenneth
Subject: Re: Fluorapophyllite-(K)
Date: 30 Oct 2021 17:50:00
Message: <web.617db7394f1e127b4cef624e6e066e29@news.povray.org>
> >
> > I'd like to discover a cheap and realistic way to add internal fractures to
> > mineral renders. Apophyllite is one of those minerals prone to being
> > found in a fractured state. I have two ideas in mind, but both are
> > rather expensive:
> > 1) height fields intersecting not only each other, but also the crystal
> > shape (which is itself an intersection); or 2) isosurfaces. Both can be
> > very, very slow. Sometimes I wish media had an ior block.
> >
> Ah... yes indeed. I have not considered your first method, but
> considered the isosurface one. However, I also cringe at the implied
> render time.
>

A beautiful crystal, Thomas-- and with those VERY nice caustics.

Long ago, I rendered a "Merry Christmas" image (which I can't find,
unfortunately), that had some objects made of translucent ice, with an ior. I
wanted internal 'cracks' to show up inside the ice-- so IIRC I accomplished that
as part of its 3-D texture, not as actual geometry. It looked decent enough to
fool the eye. Something *kind of* like this pseudo-code example:

pigment{
   gradient x
   pigment_map{
            [0.49 --ice color --]
            [0.49 bumps (?)
                 -- some scale ---
                  pigment_map{
                      [0.3 -- ice color --]
                      [0.3 rgbt <1,1,1,.7] // translucent white
                             }
                  scale 50 // to scale down the size of the warp effect
                  warp {turbulence .2}
                  scale 1/50
            ]
            [0.51 same as 0.49]
            [0.51 -- ice color --]
                 }
         }

The general idea is to have a very thin slice of translucent white (somewhat
broken up) to appear inside the ice-- like a crack or fracture. Perhaps
something similar might work for your crystal.


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From: Samuel B 
Subject: Re: Fluorapophyllite-(K)
Date: 30 Oct 2021 20:10:00
Message: <web.617ddde14f1e127bcb705ca46e741498@news.povray.org>
Thomas de Groot <tho### [at] degrootorg> wrote:
> this is a randomised version of the apophyllite crystal. I also changed
> the light probe and tweaked the scattering media (which still remains a
> second choice), and brought the photon spacing to more natural levels
> (0.01).

The shape does look more natural. But the scattering media makes it seem a bit
glowy. Maybe some absorbing media would help counteract that?

Sam


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From: Thomas de Groot
Subject: Re: Fluorapophyllite-(K)
Date: 31 Oct 2021 03:32:54
Message: <617e46a6$1@news.povray.org>
Op 30/10/2021 om 23:48 schreef Kenneth:
> 
> A beautiful crystal, Thomas-- and with those VERY nice caustics.
> 
Thank you indeed Kenneth.

> Long ago, I rendered a "Merry Christmas" image (which I can't find,
> unfortunately), that had some objects made of translucent ice, with an ior. I
> wanted internal 'cracks' to show up inside the ice-- so IIRC I accomplished that
> as part of its 3-D texture, not as actual geometry. It looked decent enough to
> fool the eye. Something *kind of* like this pseudo-code example:
> 
> pigment{
>     gradient x
>     pigment_map{
>              [0.49 --ice color --]
>              [0.49 bumps (?)
>                   -- some scale ---
>                    pigment_map{
>                        [0.3 -- ice color --]
>                        [0.3 rgbt <1,1,1,.7] // translucent white
>                               }
>                    scale 50 // to scale down the size of the warp effect
>                    warp {turbulence .2}
>                    scale 1/50
>              ]
>              [0.51 same as 0.49]
>              [0.51 -- ice color --]
>                   }
>           }
> 
> The general idea is to have a very thin slice of translucent white (somewhat
> broken up) to appear inside the ice-- like a crack or fracture. Perhaps
> something similar might work for your crystal.
> 

That is an interesting possibility which I shall try. I'll be back! 
Thanks for this!

-- 
Thomas


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From: Thomas de Groot
Subject: Re: Fluorapophyllite-(K)
Date: 31 Oct 2021 03:37:22
Message: <617e47b2$1@news.povray.org>
Op 31/10/2021 om 02:05 schreef Samuel B.:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> this is a randomised version of the apophyllite crystal. I also changed
>> the light probe and tweaked the scattering media (which still remains a
>> second choice), and brought the photon spacing to more natural levels
>> (0.01).
> 
> The shape does look more natural. But the scattering media makes it seem a bit
> glowy. Maybe some absorbing media would help counteract that?
> 
As I said, scattering is bad, and here even more so: it acts as a vulgar 
fog inside the crystal ;-)

I am currently experimenting with very tiny air bubbles as inclusions 
and distributed in a gaussian way. It looks promising but needs some 
more tweaking/thinking.

-- 
Thomas


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From: Kenneth
Subject: Re: Fluorapophyllite-(K)
Date: 31 Oct 2021 12:20:00
Message: <web.617ebba24f1e127b4cef624e6e066e29@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:
>
> Long ago, I rendered a "Merry Christmas" image...
>
> The general idea is to have a very thin slice of translucent white (somewhat
> broken up) to appear inside the ice-- like a crack or fracture. Perhaps
> something similar might work for your crystal.

I found my original scene file from 2007(!), and re-rendered one of the ice
objects. I've attached the render as the code existed then. But looking at my
code, I see that I had used simple textures for the ice cracks, bubbles,
etc-- which are just surface attributes, not 'volumetric' inside the ice. At the
time, I didn't know how to do such interior tricks... which was frustrating.

BTW, this was my actual 'crack' pigment:
pigment{
      marble // marble or wrinkles
      color_map{
           [0.0 rgbt 1]
           [0.487 rgbt 1]
           [0.492 rgbt <1,1,1,.5>]
           [0.508 rgbt <1,1,1,.5>]
           [0.513 rgbt 1]
           [1.0 rgbt 1]
                }
           warp{turbulence 4 lambda .2}
           scale 40
           warp{turbulence .5 lambda .2}
        }

But my main ice material makes use of MEDIA (as does your crystal)-- so these
'surface' pigment patterns, being 3-D of course, could be made into functions
instead, then used as additional densities or density_map(s) for the media
itself... by way of 3 color functions there, like this simplified example...
    media{
    emission <1,0,0> // for the RED channel
    density{function{PIGMENT_FUNCTION(x,y,z).red}}
         }

This way, my cracks and bubbles will show up INSIDE the ice, as I had originally
wanted. And I think that this technique might work for your crystal too. (The
interior 'bubbles' or voids you mentioned could possibly be made with 'media
voids'-- e.g., areas in the pigment/function that have rgb <0,0,0>, which would
produce NO media density there, I think. Just a guess though.)

Without your crystal post here, I would not have thought of revisiting my ice
scene with these changes. Thanks! :-)


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From: Thomas de Groot
Subject: Re: Fluorapophyllite-(K)
Date: 1 Nov 2021 03:24:55
Message: <617f9647@news.povray.org>
Op 31/10/2021 om 17:17 schreef Kenneth:
> "Kenneth" <kdw### [at] gmailcom> wrote:
>>
>> Long ago, I rendered a "Merry Christmas" image...
>>
>> The general idea is to have a very thin slice of translucent white (somewhat
>> broken up) to appear inside the ice-- like a crack or fracture. Perhaps
>> something similar might work for your crystal.
> 
> I found my original scene file from 2007(!), and re-rendered one of the ice
> objects. I've attached the render as the code existed then. But looking at my
> code, I see that I had used simple textures for the ice cracks, bubbles,
> etc-- which are just surface attributes, not 'volumetric' inside the ice. At the
> time, I didn't know how to do such interior tricks... which was frustrating.
> 
> BTW, this was my actual 'crack' pigment:
> pigment{
>        marble // marble or wrinkles
>        color_map{
>             [0.0 rgbt 1]
>             [0.487 rgbt 1]
>             [0.492 rgbt <1,1,1,.5>]
>             [0.508 rgbt <1,1,1,.5>]
>             [0.513 rgbt 1]
>             [1.0 rgbt 1]
>                  }
>             warp{turbulence 4 lambda .2}
>             scale 40
>             warp{turbulence .5 lambda .2}
>          }
> 
> But my main ice material makes use of MEDIA (as does your crystal)-- so these
> 'surface' pigment patterns, being 3-D of course, could be made into functions
> instead, then used as additional densities or density_map(s) for the media
> itself... by way of 3 color functions there, like this simplified example...
>      media{
>      emission <1,0,0> // for the RED channel
>      density{function{PIGMENT_FUNCTION(x,y,z).red}}
>           }
> 
> This way, my cracks and bubbles will show up INSIDE the ice, as I had originally
> wanted. And I think that this technique might work for your crystal too. (The
> interior 'bubbles' or voids you mentioned could possibly be made with 'media
> voids'-- e.g., areas in the pigment/function that have rgb <0,0,0>, which would
> produce NO media density there, I think. Just a guess though.)
> 
> Without your crystal post here, I would not have thought of revisiting my ice
> scene with these changes. Thanks! :-)
> 

Thanks for this Kenneth! At first glance, even these 'surface' patterns 
look great. I guess that your 'media' variant will work; I shall turn to 
that soon, as I have currently a render with 'real' bubbles (spheres, 
15000 of them) rendering. It looks good at first glance but the render 
time has dropped severely, although not dramatically. I am not yet sure 
about those 'media voids'... I shall have to think about that.

I shall make asap a scene file available and post it here. At this 
moment, it is in a terrible flux state and hardly readable, even for me. ;-)

-- 
Thomas


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From: Thomas de Groot
Subject: Re: Fluorapophyllite-(K)
Date: 1 Nov 2021 03:41:46
Message: <617f9a3a$1@news.povray.org>
Op 31/10/2021 om 08:37 schreef Thomas de Groot:
> Op 31/10/2021 om 02:05 schreef Samuel B.:
>> The shape does look more natural. But the scattering media makes it 
>> seem a bit
>> glowy. Maybe some absorbing media would help counteract that?
>>

> As I said, scattering is bad, and here even more so: it acts as a vulgar 
> fog inside the crystal ;-)
> 
> I am currently experimenting with very tiny air bubbles as inclusions 
> and distributed in a gaussian way. It looks promising but needs some 
> more tweaking/thinking.
> 

I didn't answer you fully there, I am afraid. The only media used here 
is an absorbing media which takes care of it all (with the ior too of 
course). I experimented with the scattering media in addition to the 
absorbing one, because Jaime did something like that in his crystal 
experiments.

http://www.ignorancia.org/index.php/galleries/latest-images/crystals-and-mushrooms/

However, I did not find it to work as expected.

-- 
Thomas


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From: Kenneth
Subject: Re: Fluorapophyllite-(K)
Date: 1 Nov 2021 07:30:00
Message: <web.617fcecc4f1e127b4cef624e6e066e29@news.povray.org>
Thomas de Groot <tho### [at] degrootorg> wrote:
>
> I am not yet sure about those 'media voids'... I shall have to think about that.

Yeah, I probably spoke too soon-- such voids would not produce the same visual
effect as your own method of creating voids with actual geometry.
>
> The only media used here
> is an absorbing media which takes care of it all (with the ior too of
> course). I experimented with the scattering media in addition to the
> absorbing one, because Jaime did something like that in his crystal
> experiments.
>
> http://www.ignorancia.org/index.php/galleries/latest-images/crystals-and-mushrooms/
>
> However, I did not find it to work as expected.
>

Also, it occurred to me that any fractures or cleavage planes in a crystal would
need to have some partial reflectivity (if I understand the concept of such
planes). Thin slices of interior media certainly cannot do that. :-(

BTW, thanks for the link to Jaime's crystals; I will take a look at his examples
and code.


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From: Thomas de Groot
Subject: Re: Fluorapophyllite-(K)
Date: 1 Nov 2021 08:22:02
Message: <617fdbea$1@news.povray.org>
Op 1-11-2021 om 12:26 schreef Kenneth:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>>
>> I am not yet sure about those 'media voids'... I shall have to think about that.
> 
> Yeah, I probably spoke too soon-- such voids would not produce the same visual
> effect as your own method of creating voids with actual geometry.

Correct. I am struggling with the concept however, if I would add a 
separate media to the voids (even tiny ones). The scene file I consulted 
as an example is from Glenn McCarter's Plumbing suite (2003): 
http://www.irtc.org/stills/2003-06-30.html (3rd Place) and he happily 
does mix them, but I am not really sure he is doing things correctly, 
especially now with newer pov versions.

>>
>> The only media used here
>> is an absorbing media which takes care of it all (with the ior too of
>> course). I experimented with the scattering media in addition to the
>> absorbing one, because Jaime did something like that in his crystal
>> experiments.
>>
>> http://www.ignorancia.org/index.php/galleries/latest-images/crystals-and-mushrooms/
>>
>> However, I did not find it to work as expected.
>>
> 
> Also, it occurred to me that any fractures or cleavage planes in a crystal would
> need to have some partial reflectivity (if I understand the concept of such
> planes). Thin slices of interior media certainly cannot do that. :-(
> 
Yes, there is that too. Still, I want to experiment with it to see what 
would happen.

> BTW, thanks for the link to Jaime's crystals; I will take a look at his examples
> and code.
> 
> 
Jaime's work is often a treasure trove indeed.

-- 
Thomas


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