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ť RockyTalky ť

ť 42% + 2% + 12% = 57%?

42% + 2% + 12% = 57%?

P: 7/2/2004 12:20:04 PM
Rick Rough Rock Total Posts: 15 Last Post: 12/11/2005 Member Since: 7/2/2004	Ever note that crown height %, girdle thickness %, and pavilion depth %,if recorded on a lab report, do not add up to the listed total depth %? I think the difference is due to measuring the girdle thickness between the upper and lower girdle facets, and the crown height and pavilion depth from the bezel/lower pavilion main facet area.The total depth percentage then being figured seperately by the usual method. Am I on target with this? If I am, why is it done this way? Are their other methods used where the 3 proportions equal the total depth percentage? Does it make any difference anyway? This is my first time on board! Am much enjoying everyone's comments and information. Thanks! DevilsAdvocate Rick Lewis
Posted: 7/2/2004 12:20:04 PM

There are 5 replies to this message. There are 5 replies on this page.

P: 7/2/2004 12:40:39 PM
oldminer Ideal Rock Total Posts: 4,964 Last Post: 11/20/2009 Member Since: 9/4/2000	You are onto it....It will be close but not quite exact. One factor to consider it with round diamonds one is using the average of the diameter, not the minimum or maximum. The depth measurement is exact. However, the crown height, girdle thickness and pavilion depths are all based on relative average measurements. This leads to a small compromise in accuracy. ALso the thckness of the girdle being measured in some inconsistent manner, like you mentioned,is another component of this small measurement problem. David S. Atlas GG(GIA), ASG, Sr. Mbr. NAJA www.datlas.com
Posted: 7/2/2004 12:40:39 PM

P: 7/2/2004 1:08:49 PM
niceice Ideal Rock Total Posts: 1,792 Last Post: 7/22/2008 Member Since: 1/29/2003	Excellent answer Dave... And just in case the point was missed, we'll expand on it a bit more. The Sarin and OGI machines actually measure the Crown and Pavilion angle measurements, but calculate the Crown Height and Pavilion Depth measurements based upon the averages, so there tends to be a lot of spread in those measurements... This fact can be verified by calling any of the major gemological laboratories, Sarin or OGI. Todd L. Gray, President NiceIce.com
Posted: 7/2/2004 1:08:49 PM

P: 7/2/2004 1:22:50 PM
Superidealist Ideal Rock Total Posts: 655 Last Post: 8/23/2006 Member Since: 9/10/2003	Consider also that 42.4% + 2.1% + 12.3% = 56.8% rounded to the nearest percent would be 42% + 2% + 12% = 57%. D Riley
Posted: 7/2/2004 1:22:50 PM

P: 7/4/2004 11:30:05 AM
Rick Rough Rock Total Posts: 15 Last Post: 12/11/2005 Member Since: 7/2/2004	---------------- On 7/2/2004 12:40:39 PM oldminer wrote: You are onto it....It will be close but not quite exact. One factor to consider it with round diamonds one is using the average of the diameter, not the minimum or maximum. The depth measurement is exact. However, the crown height, girdle thickness and pavilion depths are all based on relative average measurements. This leads to a small compromise in accuracy. ALso the thckness of the girdle being measured in some inconsistent manner, like you mentioned,is another component of this small measurement problem.---------------- David, Robin & Todd, and D. Riley, Thank you for responding to my questions. I know that percentages can jump when used decimal places are added together, then rounded up. The example I used is actual, and I did so for simplicity. Most of the reports recording the 3 percentages do go into decimal places, but still do not add up to the listed total depth percentage. Once agai, I apreciate all your replies! I have learned some good thigs on this site and am looking forward to getting more involved. Rick Lewis
Posted: 7/4/2004 11:30:05 AM

P: 7/4/2004 4:34:48 PM
Garry H (Cut Nut) Ideal Rock Total Posts: 11,581 Last Post: 11/23/2009 Member Since: 8/16/2000	DA there should be about 1.7% error because of the position that US labs measure the girdle thickenss. It is as you suggested - between the bones of the facet junctions - in the valley where it is thinnest. The thicker part where the main or bezel facets meet is indeed where the crown and pavilion averages are taken. Garry Holloway FGAA DipDT HCA and Ideal-scope developer http://www.ideal-scope.com and http://www.HollowayDiamonds.com.au
Posted: 7/4/2004 4:34:48 PM

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