Firescope Flaw?

[Superidealist]

Interpretation of Firescope-like images assumes the following two principles:

i) White light enters through the diamond’s pavilion.
ii) Red light enters through the diamond’s crown.

To drastically oversimplify, white is bad because it represents light leakage through the pavilion and red is good because it represents light returned through the crown.

The interior of a Firescope-like device is red above the girdle plane and white or black below. (For the sake of simplicity, let us assume the lower interior to be white.) Herein lies a problem. The geometry of the diamond and the design of the device cause the violation of items i and ii, above.

The first graphic represents a diamond within a Firescope-like device. The upper interior surfaces of the device lying in the red shaded region allow red light to enter through the diamond’s pavilion, while the lower interior surfaces of the device lying in the yellow shaded region allow white light to enter through the diamond’s crown. Red light entering through the pavilion in manner such that it is visible to the viewer would be interpreted as light return when it truly represents light leakage. White light entering through the crown in manner such that it is visible to the viewer would be interpreted as light leakage when it truly represents light return.

The second graphic illustrates a proposal to reduce this effect. Imagine a sticker in the shape of an annulus, red above and white below, surrounding the diamond in the device’s tray. The sticker would block much (but not all) of the light from the problem regions while returning red light to the crown and white light to the pavilion.

 

[Superidealist]

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[Superidealist]

To clarify, the measure of the red shaded angle is equal to the measure of the diamond's pavilion angle, while the measure of the yellow shaded angle is equal to the measure of the diamond's crown angle.

 

[valeria101]

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On 5/19/2004 11:16:03 PM Superidealist wrote:



The upper interior surfaces of the device lying in the red shaded region allow red light to enter through the diamond’s pavilion, while the lower interior surfaces of the device lying in the yellow shaded region allow white light to enter through the diamond’s crown.

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Not sure I understand how this works... can you plot the culprit reflection path on the pic?

 

[Garry H (Cut Nut)]

SI you are being very precise today

Actually very little light form either direction will have very little effect.
The ray trace here shows that what light that would emegre from the crown would not be seen by an Ideal-scope / FS observer.
But the ligth that could come from this direction could and does contribute to fire because the light that does get in the pavilion enters close to the critical angle creating great dispersion.

 

[Garry H (Cut Nut)]

And light from below will either reflect off (not so interesting) or leak out the pavilion. none of this light would be visible through the ideal-scope.

In this latter case the only critique GIA ever published (letter to Editor) about their Brilliance study in was written by Marty Haske and it was a waste of ink because of what you can see here.

If you want to experiment with these concepts simply sit a loose diamond on some very bright paper and see what you can see from various directions. I showed Marty this in 1999.

 

[verticalhorizon]

Thanks CutNut... Those diagrams were great!

So then, by simply holding the diamond to a IdealScope/Lightscope type tool, you're not really letting in white light from the pavillion, you're seeing THROUGH the diamond to the light on the other side. Whereas the red you see is a reflection of the internal facets acting as mirrors of the tool itself. Yes?

 

[Superidealist]

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On 5/20/2004 6:06:29 AM Garry H (Cut Nut) wrote:

Actually very little light form either direction will have very little effect.----------------

I doubted that the effect would be significant because of the shallow angles of incidence but, not knowing enough to do the raytracing, I figured I'd leave it to you or Serg to correct me.

A more significant effect occurs when the lower interior is black instead of white, since this allows a greater angle of incidence (from the lower interior to the pavilion).

 

[Garry H (Cut Nut)]

you mean the blackened walls of the firescope(R) ?

 

[Superidealist]

Yes.