Please explain "Depth" & "Table" in plain english.

[brennerd]

Will somebody explain to me how to interpret depth and table, and what they mean in plain english (i.e. impact on heigth of the diamond, diameter, etc.). Thanks.

 

[pricescope]

Table and depth as well as culet and often girdle are measured as % from girdle diameter.

 

[aljdewey]

The table is the top, flat plane of a diamond in the face-up position.




The depth is the measurement of the diamond from the table to the culet (as though you drew a line from the culet that runs perpendicular to the table).




Both measurements, as Leonid stated, are measured as a percentage of the diameter of a diamond (which is the girdle - the widest part).




In concert with crown/pavilion angles, this information tells you how the facets align with one another. Think of a diamond like the mirror funhouse at a carnival. The mirrors have to be arranged relative to one another to produce a desired effect......to make you legs look 6 ft long or to make your stomach to look wide.




If you move one of those mirrors a degree or two, you don't get your full reflection back in the same way....so your legs may now look 3 ft long instead of 6 ft long.




Same thing with a diamond. The facets should ideally be arranged in such a way that the diamond returns a maximum amount of light. When that arrangement is altered, it creates opportunities for light to leak out of the diamond instead of returning back to the eye of the person viewing it.




A diamond that is too deep will leak light, and the table size affects how that light looks when returned, too.




Hope this helps.

 

[Rhino]

Good points al. (btw I'd like a consumers critique on my minor facets page if you don't mind

)




One thing I would emphasize about table and total depth measurements ....




Even when they seem to be good THIS DOES NOT guarantee a beautiful diamond. At a very minimum crown and pavilion angles must be known.





That's all!

Rhino

 

[hoorray]

So, if you have 2 well cut RBs (<2 on the HCA), one with a 55% table and one with a 57% table, will they look substantially different, or is this close enough that it won't matter? I've heard people say they prefer smaller tables, but I've never seen a crisp description of the impact the table size has on fire, scint., etc.

 

[flyingharp]

OK, here's my attempt at being scientific (and I am more than willing to be corrected on any point

):

Brilliance is a subjective measurement comprising a few distinct optical processes:

1. External lustre ("shininess")- how much external light is "absorbed" into the body of the diamond and how much is reflected.

2. Internal brilliance - based on refraction (bending of light) in the stone, which in turn depends on depth of the pavillion. Too shallow - light leaks out the bottom, too deep - light leaks out the side. Either way, light doesn't get "reflected" back at you through the crown.

3. Dispersion "fire" - rainbow colours caused by the prism effect of the crown facets and directly dependent upon their size. Large crown facets = lots of mini-rainbows. Here is the trade-off: larger crown facets = more dispersion = smaller table size = less brilliance ('cos less space for reflected light to leave through the top/table)

4. Scintillation - twinkling reflections when you move the stone or light source. Depends on number of reflections from facets - lots of smaller facets = more reflections vs fewer larger facets = less reflections ("lifeless" diamond) Large table size = smaller facets

How does all that sound?

 

[Rhino]

One of the things that can get really confusing about the HCA is that you can have diamonds that have higher scores 1.6 - 1.8 be more attractive that stones with seemingly better scores .3 - .6. What can be even more confusing is you can have 2 stones that have identical HCA scores yet look as different as the 2 stones below simply by changing the minor facet arrangement. Both of these diamonds have identical crown/pavilion/table data (the data you'd typically get from a Sarin or MegaScope report yet the minor facets (40 in all which are most commonly NOT reported) can change the appearance from one stone to another quite dramatically as demonstrated here.




/idealbb/files/sameHCA.gif




Here are simulated LightScope images of the 2 stones.




/idealbb/files/samehcals.gif




Anyone who has studied our pages on how to interpret these images knows there will be a difference in the optical qualities between the 2 stones and this is assuming extremely high symmetry in each stone which is not the case 99% of the time. Variances in the crown angles, pavilion angles, & lower girdles can dramatically affect appearance as well which would make the optical symmetry very chaotic and choppy.




Similar to this stone.


/idealbb/files/71evs2-lts[1].jpg




In short the HCA is good as a basic (very basic) preliminary tool for weeding out stones that will be good reflectors vs bad reflectors of light. Intensity of that light return, scintillation, symmetry, affect of minor facets and their impact upon the look of the stone and contrast brilliance/scintillation are impossible to assess with it though and all of these factors affect the appearance of a diamond and it's overall beauty.




My .02c


Rhino

 

[Colored Gemstone Nut]

----------------
On 10/25/2003 6:04:45 PM lop wrote:











So, if you have 2 well cut RBs (----------------

Strong fire can exist in a diamond with a larger table as long as the crown/pavilion angle combination is at the critical point of producing the best results. Having a larger table in a diamond can contribute to more leakage. Overall brilliance includes refracted light with a combination of reflected light viewed off a diamonds facet surfaces. Diamonds which have larger tables will increase the reflected light off the table which is only considered white light return. Fire & Dispersion originate within the diamond and are most obvious in direct & ambient light conditions. Diamonds with smaller tables have less reflected light and more refracted light. Other things to take into account are the tweaking of minor facets which has been argued can accent the overall fire, brilliance & scintillation.

/idealbb/images/smilies/wavey.gif

 

[hoorray]

Thanks Josh,

That makes sense. I've just been befuddled because there is so much focus on crown/pav angles (which I understand), but within the general AGS0 range, I've struggled to understand how small differneces in the different proportions impact performance.

 

[hoorray]

whoops, hit submit too soon...

so as an unscientific description, that's pretty good flyingharp. For me, putting it all together, and understanding the small differneces is the hard part. and as you point out Rhino, that's just the beginning...

 

[Rhino]

Right lop. Only the beginning. There is so much more that goes into determining both beauty & value in a diamond than just getting an HCA #. One reason why some companies do not like it (particularly some super ideal brands I know of) is becuase it can make a diamond with really nasty optical symmetry appear to be as beautiful as one with incredible precision and the fact of the matter is these super ideal companies are right. The beauty in the 2 stones will not be the same even though they get same or similar HCA scores.




Rhino

 

[hoorray]

So Rhino....

there was a diversion in a thread here about dogs (which I can't find...). We don't have a dog since we've always traveled too much with work to be a good home for a dog. But...if I had one, I want yours! what a great looking dog!