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Hi everyone: I am trying to practice rendering gemstones and am having a bit of difficulty with the sapphire IOR. The problem is that when I apply the IOR file from the material wizard to my gemstone the colour is a very light blue when compared to the sphere in the IOR wizard. I thought that it had something to do with the attenuation distance so I unlocked the ior and cut it in half but had the same result. Do you guys have any thoughts? I just rendered the stone on some white plastic. Here are a couple of shots

Straight ior file



Attenuation distance cut in half



Thanks in advance
Cary

Hi Cary,

It seems you may have misunderstood complex ior files. A complex ior file fully-describes the BSDF's reflectance and transmittance properties - that is why the reflectance panel is disabled when you specify one of these files. So it is an either/or situation, and switching the file off, changing transmittance, and then switching back on the file will have no effect - whenever you use a file, you are not going to be using any of the other parameters at all.

As to the actual results from using the sapphire ior file, I am underqualified in this area to offer an opinion - maybe one of the gem people will chime in.

Cheers,

JD

that way I may get more hits.
Cary

what is the scale/size of your gem?

if you are using the ior-file, you kind of lock your attunuation distance, it only referes then to the actual size of your gem.

Hi Firebird: The gem is around 10mm in diameter. What do you mean by
"you kind of lock your attenuation distance"?
Thanks
Cary

Maxwell renderers look much better in scales of metres or larger...scale your scene up just for the render

Silverblade-T-E wrote:Maxwell renderers look much better in scales of metres or larger...scale your scene up just for the render

I'd like to think Maxwell is a realistic non-biased render. Hence, this should work without having to trick the program.

I have a strange suspicion that the ior was meant for a faint or light blue sapphire, not a deep blue sapphire.

I'd like to think Maxwell is a realistic non-biased render. Hence, this should work without having to trick the program.

Sorry, but that conclusion is illogical. IOR files generally come from scientifically-measured data, but this one was created by hand (by hdesbois) using data from this page. So, I don't really think you can use it to comment on Maxwell's ability to produce realistic results. You could easily write 'sapphire' in a text-document, save it with the .ior extension, load it into a material, and come up with a result that's doesn't look like a sapphire - this also would not reflect on abilities of the engine.

I found the original post about this IOR: http://www.maxwellrender.com/forum/view ... 585#170585 ...it is noted there:

Remarks: Material is scale sensitive. If it comes a bit too clear on gemstone sized object, use a spreadsheet to multiply the second column by 1.5 to 3 or 4.

So Silverblade is correct? I will try to scale up the sapphire and then try the ior file again. Thanks
Cary

It' not what I'd do, although it will make a difference. If you change the scale, you'll change the DOF characteristics of the camera, and the calibration of your scene lighting...I'd do like the author of the file said and try modifying the ior data.

JDHill wrote:

I'd like to think Maxwell is a realistic non-biased render. Hence, this should work without having to trick the program.

Sorry, but that conclusion is illogical. IOR files generally come from scientifically-measured data, but this one was created by hand (by hdesbois) using data from this page. So, I don't really think you can use it to comment on Maxwell's ability to produce realistic results. You could easily write 'sapphire' in a text-document, save it with the .ior extension, load it into a material, and come up with a result that's doesn't look like a sapphire - this also would not reflect on abilities of the engine.

I found the original post about this IOR: http://www.maxwellrender.com/forum/view ... 585#170585 ...it is noted there:

Remarks: Material is scale sensitive. If it comes a bit too clear on gemstone sized object, use a spreadsheet to multiply the second column by 1.5 to 3 or 4.

The data is only as good as the specimen it was collected from. I'm not arguing that the data is incorrect, I think the specimen is not the typical deep sapphire you normally see. This is just a hunch. The specimen might have been large, hence the faintness on small gemstones. Multiplying the data by a factor would solve the problem, thanks for the quote.