关于mahenge尖晶的优化处理

一直以来，大家认为在尖晶方面，优化处理的很少。确实，普通尖晶一般不值得去改色、改净度。但在坦桑尼亚，有一种可以媲美帕拉伊巴霓虹蓝碧玺的霓虹粉尖晶出世后，倍受人们瞩目。说实话，mahenge尖晶一直以来都是欧美人的最爱，一直被欧美人收购和把持。加之断矿和产量的限制，流入国内十分稀少。

于是，这就给了不良商人以机会，在坦桑尼亚本地诞生了众多优化粉尖晶，颜色从淡粉到深粉或者粉色到红色的改色。
XIX. Traitement du Spinelle :

- Violet => Jaune.
- Rouge => Rouge plus intense.

以上是国外网站的优化手段，紫色变黄色，红色变深。
早在2005年，业内就有担心唯一的净土---尖晶会被优化处理，于是GIA在2009年出了一份报告《Distinguishing Heated Spinels from Unheated Natural Spinels and from Synthetic Spinels》
Abstract
Natural spinels are found in colors equal to those of fine rubies or sapphires, and
since top quality spinels are one of the few ‘better known’ gems to have so far
escaped the attention of large scale treatment processes; they are gaining a greater
commercial importance. However, it would appear that at least some heat treated
natural spinels are on the market and therefore it is important that criteria be
established for the separation of the treated from the natural material. This paper
reviews, confirms, and extends the original identification criteria developed during
experiments carried out in 2005 on pink to red spinel from Tanzania and applies
these criteria to a wide variety of spinels from a variety of sources.

从图中可以看出，尖晶在1400度的高温后，颜色明显变暗。而之前的加热处理手段，由于没有达到这个温度，仅能改变尖晶的净度，但很不幸，在1400度高温后，尖晶颜色也遭到改变。
Conclusions
Unheated natural spinel is easily separated from heated natural spinel or synthetic
spinel by examining the width of the 405 cm
‐1
Raman line, or by examining the width
of the zero phonon line of the Cr
3+
PL spectrum in stones containing sufficient
chromium. Separating inclusion free heated natural spinel from some synthetic
spinels requires examining the trace element chemistry with EDXRF and LA‐ICP‐MS
where the differences become quite clear. These techniques have been in routine
use in GIA’s laboratories for well over a year. Further and more comprehensive data
will be published as research continues.
We would like to thank Hans‐Georg Wild, Markus Wild and Gamini Zoysa for
providing a wide variety of rough spinel for this research. In addition we would like
to thank Milan Kokta and Jennifer Stone‐Sundberg of St. Gobain Crystals and
Detectors for a much appreciated tutorial on synthetic spinel.

最后GIA的结论，加热可以改变净度，颜色很难改变，但是，谁敢保证这些年兰卡人和泰国人没做过什么呢。这份报告主要说明优化尖晶和合成尖晶还是很好区分的，对于优化尖晶和自然尖晶,GIA更是拥有很多的光谱数据去检测，这个业内无须担心。国检？它可以给我们大家说明，这块宝石是真是假，关于是否优化的评论（comments），我常常看到的是空白……
人在国外，经常看看一些国外的珠宝论坛，发现国外有很多朋友真正在讨论珠宝的专业知识，从光谱研究到辐照用哪种光源，我看的是叹为观止……国内大多数是晒货、卖货……真正对于彩宝的研究，寥寥可数……
As an ending note, it is unfortunate
that as a gemstone which has
traditionally been exempt from
controversy involving treatment,
spinel must now be added to the long
list of gemstones that may be heated.
Furthermore, this is another reminder
that as gemologists, we can no longer
take any gem for granted as being
“untreated.”
国外论坛网友的论文结尾，证明尖晶存在部分优化的可能，提醒我们不要再想当然的认为任何宝石都是无优化的。
In terms of treatments to Spinels, they can be oiled, there's new evidence that some are being diffused and black spinel may even be coated! Here's a couple of articles on the heat treatment of spinels. I'm not sure if there is much of a price difference between unheated and heated spinel. If there is, I wouldn't think it would be much as these are more "collector" stones than one that Joe Public will rush into a jeweller and ask about.
最后，参考各大国外论坛和问了一个当地的坦桑尼亚宝石商人，他说，坦桑尼亚有注色尖晶，他虽然不知道如何注色（国外论坛说是OIL，注油的意思？），但他确信有。在矿区，一块颜色正宗的mahenge樱桃红尖晶原石，1g左右（可以切出2克拉）售价高达1000000-200000先令（4000-8000人民币），而且供不应求，大多数欧美人把持并且迅速买走。想到此，国内有一个精于此行业的朋友，跟我炫耀说道，从坦桑尼亚本国商人批发的樱桃红尖晶成品，包邮到国内XXX人民币一克拉，不禁莞尔一笑。