Brilliance/sparkle of sapphire v. spinel.

[beaujolais]

How do you compare the brilliance/sparkle of a sapphire v. spinel?

Thanks.

 

[Pieface]

This page has some interesting info on dispersion in gems which leads to "fire"

dispersion

Lustre and Refractive index are also similar. There are quite a few famous rubies (a form of corundum like sapphire) that have turned out to be spinels...I would say that they probably perform very similarly to each other, at least to the lay-person, when factors like clarity, cut and polish are the same.

Of course I am pretty inexperienced so take with a grain of salt

 

[beaujolais]

Great article, Pie. Thanks so much.

So the brilliance/scintillation (sparkle) are similar in both types of stone?

 

[colormyworld]

They are very similar. Sapphire has a slightly higher RI. Spinel will show more rainbow colors as dispersion is slightly higher.

To me the real difference is in the way each displays thier colors. Spinels color seem" harder" more defined. More meatalic looking. I think it is due to them being SR. Sapphires on the other hand have a cloudy essence to the colors. I don''t mean the stone is cloudy but the color is not as pure looking as spinels. IMO I guess another way to describe this would be to say that to me sapphires look warmer while spinels color looks colder. I really like them both but perfer the look of spinels.

 

[Pieface]

Interesting point CMW. I think I understand what you are saying. I know I have seen some stones, zircons and sphenes mostly, that give me a headache to look at with their extra refraction.

 

[DiamondExpert]

...and corundum is doubly refractive, while spinel is singly refractive.

 

[beaujolais]

What does doubly refractive mean? I just did a Google search for it and I found very technical info. that I''m not able to apply. Can someone explain it simply? Thanks.

 

[colormyworld]

When light enters a DR stone it is bent and divided into two rays.

 

[DiamondExpert]

It means that when light (unpolarized) enters a gemstone (any crystalline form but cubic - diamond,spinel) it is split (into 2 rays, polarized at right angles) and each travels at a slightly different speed through the crystal, each being refracted (deflected) to different extents according to the ratio of the speed of that light ray in air vs. its speed in the material.

In singly refractive material, the light is not split into two rays (it travels the same speed in all directions), and the single ray is singly refracted according to the ratio of the speed of that light in air vs. its speed in the material.

RI varies for each wavelength of light, the higher energy (violet/blue) being refracted more than the lower energy (red) - this is how the spectral light (dispersion) flashes are generated. So a monochromatic wavelength (Sodium light ~589nm) is used as a standard.

 

[beaujolais]

Oh dear - so let me interpret that:

so singley refractive is better and single refractives will give off more light?

Is that it?

Thanks.

 

[DiamondExpert]

no

 

[beaujolais]

then double refractive is better & will give off more light?

help !

please

 

[Pieface]

I think they are unrelated sonoma. Light/brilliance is going to come down to the cutter understanding the material and cutting it according to its properties to achieve this. I don''t think that any one material is inherently more brilliant than another provided they are equal clarity etc. Some stones certainly are more dispersive than others but I think total light return is down to the cutter getting all his ducks in a row.

 

[beaujolais]

Thanks Pie. That''s what I was looking for.