Bill Hails <me### [at] billhailsnet> wrote:
> Hi.
> I'm trying to model a pearl, well, lots of them eventually.

Oh, good. They'll go well with my diamonds. :)

> I found a nice reference photo on the web.
>
> http://www.loppleman.com/pearls_white.jpg
>
> but so far I'm having difficulty. What I've got so far is,
> to paraphrase: almost, but not quite, completely unlike a pearl.
>
> http://billhails.net/Pearl.png

That's not too bad, it's just a bit too glassy or metallic, IMHO. But it's
almost impossible to model shiny things properly in a bare scene. Follow
your reference image's example and give your pearl some things to reflect.
Other pearls would be ideal, but for development work, just throw in a few
metal balls and rings, and maybe use a simple lightprobe (or just an
environment sphere with no HDRI).

> That's done with lots of nested semitransparent spheres
> and the render time is already feeling painful (around five
> minutes for that pic,) considering I'll be doing lots of them.

Nested spheres never do what you want them to. I tried doing clouds with
them once... :)

> I don't want to steal a ready-made texture, I'd rather gain the
> experience and roll my own, but hints would be welcome.

Ok, here's a few ideas off the top of my head.  Try using a scattering
media, with a reflective layer below it. I think that will eliminate the
need for most of your spheres. I don't use media much at 566MHz, so you'll
have to ask the media experts about the fine art of subsurface scattering.

Vary brilliance: try .5-10, but really high values can give interesting
effects, too. Try using both phong and specular. Phong for the general
'glow' of the pearl and specular for the actual highlight spot. Just keep
the total of phong+specular less than one. Even try using a non-zero
ambient. It should be ok here, even if you are using radiosity, since
pearls always seem to have a bit of a glow about them.

I think pearl has a fairly high IOR, but I can't seem to find a value for
it... I guess it's pretty hard to measure properly with all those layers.

Good luck, Bill!

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