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Dates/References on Lessons & Articles


As I work my way through the Professional Gemologist course, I find myself asking when a particular lesson or article was last updated. My reason for wanting to know is because of conflicting statements in various reference materials.

A case in point is Unit 2, Lesson 8, HPHT Diamond Update. When was this update current? The lesson refers crystal lattice shift corrections and HPHT:

“Some theories suggest that type IIa diamonds have a stressed growth, atomic lattice shift, caused by volcanic eruption, and that this shift is corrected under HPHT. The Gubelin Gem Lab found this to be false.”

What I’d like to do is be able to look up the Gubelin reference, or at least know when it was published so I can better assess differences in other references. In this particular case, the following not particularly old article from January 2015 (fig 5 “HPHT heals deformations/broken bonds.”):

M&A Gemological Instruments - Diamond Classification

These statements seem to be in direct conflict, yet I have no way to directly compare them, short of chasing down the Gubelin reference.


The Donald Clark HPHT Diamond article predates 2013, I’ll see if I can find a more exact time of publication. This article has not been significantly updated since then.

However, I believe the study by the Gubelin Gem Lab on HPHT Mr. Clark references is from 2000. Those results are specifically mentioned in this JCK article from October 2000, and I think this GIA article from Fall 2000 discusses these findings (p. 209 specifically refers to the test results on lattice distortion).


Thank you Pedro. Looking forward to reading these. Even though they pre-date the M&A document, I guess there’s still the question of whether M&A is keeping up to date.



Best estimate for the original publication date of the Donald Clark HPHT article is between Oct 2000 and July 2001.


Thanks again.

In a broader sense, has there been any thought about adding dates more generally to lessons so students have a better idea of the age of the materials? I ask, because one of the recurring themes in the course is how gemology is constantly changing with new techniques with regard to analysis, synthetics, and methods for detection, etc.