Refractive Index
by
Alphabetical Listing of Material

 
Refractive Index
by
Increasing RI Value
Material
RI
 
Material
RI
         
Air (STP) 1.00029   Vacuum 1.00000
Amethyst (Quartz) 1.54 (+1.55)   Air (STP)
1.00029
Beryl (Emerald) 1.57 (+1.60)   Water 1.333
Citrine 1.55   Glass 1.517
Corundum (Ruby, Sapphire) 1.76 (+1.77)   Quartz 1.54 (+1.55)
Emerald (Beryl) 1.57 (+1.60)   Amethyst (Quartz) 1.54 (+1.55)
Diamond 2.417   Rock Crystal (Quartz) 1.54 (+1.55)
Garnet (Pyropes) 1.73-1.75   Citrine 1.55
Garnet (Almandine) 1.76-1.83   Beryl (Emerald) 1.57 (+1.60)
Garnet (Rhodolite) 1.76   Emerald (Beryl) 1.57 (+1.60)
Glass 1.517   Topaz 1.61 (+1.62)
Peridot (Olivine) 1.65 (+1.69)   Tourmaline 1.62 (+1.64)
Quartz 1.54 (+1.55)   Peridot (Olivine) 1.65 (+1.69)
Rock Crystal (Quartz) 1.54 (+1.55)   Garnet (Pyropes) 1.73-1.75
Ruby (Corundum) 1.76 (+1.77)   Garnet (Rhodolite) 1.76
Sapphire (Corundum) 1.76 (+1.77)   Garnet (Almandine) 1.76-1.83
Topaz 1.61 (+1.62)   Ruby (Corundum) 1.76 (+1.77)
Tourmaline 1.62 (+1.64)   Sapphire (Corundum) 1.76 (+1.77)
Vacuum 1.00000   Corundum (Ruby, Sapphire) 1.76 (+1.77)
Water 1.333   'High' Zircon 1.96 (+2.01)
High' Zircon 1.96 (+2.01)   Diamond 2.417
         
         
(Note: Refractive Index listings which have two numbers [ex. 1.54 (+1.55)] denote materials with double refraction properties. For ease of rendering the material in a 3D program, simply use the first number to set the refraction property.)
         

For more detailed articles on these topics, Bob Keller has several clear, but detailed, explanations available at his site. While these are geared toward actual lapidary situations, they do contain information which can be applied to 3D rendering. Two of the more relevant ones are:

PROPERTIES OF COMMONLY FACETED MINERALS AND MATERIALS

REFRACTIVE INDEX AND CRITICAL ANGLE

         

 

So, what does it mean to have a particular refractive index applied to a model in a 3D program?
Below are examples of RI values applied to a single model, with no other changes made to the render.
(For sake of comparison, normally colored stones are rendered without color to emphasize the effect of refraction.)


Air/Vacuum RI=1.00

 


Water RI=1.33

 


Glass RI=1.517

 


Quartz RI=1.54

 


Emerald RI=1.57

 


Topaz RI=1.61

 


Garnet RI=1.76

 


Zircon RI=1.96

 


Diamond RI=2.42

 

As you can see, between very close settings there isn't much difference immediately visible. However, if a gemstone's angles are selected to fit the RI of, say, quartz, then the angles for a diamond might not show all the sparkle and flash desired.

How does a 3D modeller deal with this?
The simplest way, is to leave the model's RI as specified and only change the color and transparence to match the 'look' of the gem you want.
On the other hand, if you know the RI the design is made for and want to use the actual RI of a specific gem type (and I tried to make note of these as much as possible), is to stretch or shrink the model on the Y axis (and ONLY the Y axis). Make sure the stone is set in your modelling program so the Y axis runs from the flat top (the table) down through the bottom point (the culet), then *ever-so-slightly* increase the vertical size if you want to use an RI greater then what the model was made for, or conversely, slightly decrease the vertical scale if you want to use an RI less than the model's original. This is trial and error time, so go for a compromise between convenience, accuracy and enjoyment.

Be aware of one major problem with most 3D programs I have seen or heard of so far. They do NOT, repeat, do NOT calculate -all- true optical qualities. (Some of the *very, very* high-end programs might, but most widely available 3D programs can't.) While the gem model itself will *internally* show effects of refraction, the light that 'passes through' the model and come out to the other side unaffected by it's trip inside the gem. Things like rainbow flashes around the gem simply have to be faked in one fashion or another--and that's a whole 'nuther' website in itself!