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Op 29-10-2021 om 12:49 schreef Bald Eagle:
> "Samuel B." <stb### [at] hotmail com> wrote:
>> Thomas de Groot <tho### [at] degrootorg> wrote:
>
>>> [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.
>
> I would imagine that it might have something to do with the phase diagram of the
> material. Freeze the material so that it's solid, and then do a melting-point
> test by the usual slow heating. Maybe there's some specialized
> pressure-temperature nomograph that's been developed for this type of thing...
>
Yes, I think it was phase changes indeed. All that happened 45 years ago...
--
Thomas
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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).
--
Thomas
Post a reply to this message
Attachments:
Download 'krystalshaper_apophyllite_005c.jpg' (56 KB)
Preview of image 'krystalshaper_apophyllite_005c.jpg'
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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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> >
> > 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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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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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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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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"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! :-)
Post a reply to this message
Attachments:
Download 'pov_logo_as_ice.jpg' (56 KB)
Preview of image 'pov_logo_as_ice.jpg'
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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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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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