Calling Garry...& other experts...

[surfgirl]

Okay, here''s what I''m working on right now...(actually I''m avoiding work!)...Because my stone is old and has never been to the "spa" (aka "lab"), I cant plug in all the groovy numbers into the HCA to see how it scores (though I know it scores top marks with my eyes!). Is there any way to guesstimate the percentages that one needs based on depth, table and the dimensions? What I do know is this:

Dimensions: 8.85 x 8.80 x 5.21
Depth: 59.61%
Table: 58.0%

Is there any way to guesstimate the other numbers required to plug into the HCA table? Thanks to anyone if they can figure this out!

 

[chrono]

Surf,
A non-expert opinion coming up:

Mathematically, I don''t think it is possible. Knowng the table and depth is a start, but the crown and pavilion combo could be anything. The angles work together so it could be high crown, low pavilion or low crown, high pavilion, or medium crown, medium pavilion. I''m not explaining this clearly, am I?

In any case, since it is a combo, it is not possible to know one without the other.

 

[surfgirl]

Thanks for the reply Chrono...Shoot! Can you only get all those angles if the stone is removed from the setting or can you measure that sort of thing in the setting (keeping in mind my center stone is completely accessible in it''s setting)? I really wanted to play with that HCA...

 

[chrono]

I think the only way to get the angles is to have the unset stone measured by a Sarin machine. Sorry.

 

[JohnQuixote]

Date: 10/17/2007 4:02:52 PM
Author: surfgirl
Thanks for the reply Chrono...Shoot! Can you only get all those angles if the stone is removed from the setting or can you measure that sort of thing in the setting (keeping in mind my center stone is completely accessible in it's setting)? I really wanted to play with that HCA...

We can help SG. Do you have a clear zoomed photo looking straight down onto the diamond? If you have one in diffused or darkfield light (darkfield = illuminated from sides) we should be able to see your table reflection, which is how cranky old porch-sitting gemologists used to judge pavilion angle back in the days before these newfangled Sarin machines. We can also import the photo into DC to get a reasonable idea about minors and CA. If you know girdle thickness we can be more accurate.

An appraiser we know has a more precise way of getting GT/CA but it may be proprietary - and I don't want to be locked out of the clubhouse for spilling the beans.

 

[surfgirl]

Thanks John! Well, I''ll have to re-photograph the stone from the top with side lighting and see what I can do. I''ll re post here when I get a good shot. Thanks for the idea...

 

[chrono]

I'm glad there's other ways to find the CA and PA without removal of the stone from the setting. I'll be keeping my eye out on this thread, Surf. I'm really curious too.

 

[JohnQuixote]

Don't expect pinpoint accuracy. Within 0.2 deg PA and 0.3-0.4 degCA is possible as I recall, especially if we know depth/gt. We first messed around with this stuff in 04. Sergey is a rock star.