Thermal Conductivity

With the rapid advancements in the field of crystal growth in the past several years, materials produced for the purpose of simulating diamond have become more and more difficult to detect. Because the R.I’s (refractive index) of diamond and most simulants are over the limit of the conventional refracatometer, identification is more difficult.

In 1978, the Ceres Corporation, which is a large manufacturer of synthetic cubic zirconia, came out with completely new type of instrument for the separation of diamond from the various simulants. The instrument is termed a ‘thermal conductivity probe’ and operates on the principle of thermal (heat) conductivity. Diamond is unique in this property and even the most impure Type I stones still conduct heat many times quicker than the next best material.

Since the Ceres probe was developed many other companies have also developed similar instruments. They usually consist of a small box with a meter or lights to indicate whether or not the stone is diamond. A pen-like probe is attached to the box by a wire. The conductivity of the stone is tested by pressing the copper tip of the probe against the stone. An electrical current is passed through a thermister in contact with the stone which heats it up slightly. Then the current is cut off and sensors measure the speed with which it cools. Diamond, having the highest thermal conductivity, cools tip faster than any other material.

The advantages of the thermal conductivity probe are many. Any size stone from 0.03 carat up can be tested, mounted or unmounted. The quality of the polish or thin surface coatings does not affect the accuracy.

Advantages
- Stones down to 0.03 carat can be tested.
- Mounted or unmounted stones can be tested.
- Faceted or rough stones can be tested.
- Doublets can be tested if several parts of the stone are checked.
- Thin surface coatings on the stone do not affect the accuracy.
- Each stone takes only about 3 seconds to test.
- The test is extremely accurate, especially for materials which closely resemble diamond in appearance.

Disadvantages
- The probe only indicates whether or not a stone is diamond. It does not distinguish between various simulants.
- As with any instrument, there is chance for error if it is not used properly or if it was manufactured poorly.

The thermal conductivity probes offer the gemologist an accurate and quick means of distinguishing between diamond and its simulants. If used properly by a trained gemologist, the results are both accurate and repeatable.

Scheelite

Chemistry: Calcium tungstate.
Crystal system: Tetragonal; dipyramids (may look like octahedral) or tabular crystals, also granular masses.
Color: Transparent to translucent; colorless, brown, orange, yellow, purple.
Hardness: 4.5 - 5
Cleavage: Perfect: 1 direction: fracture: splintery, sub-conchoidal to uneven.
Specific gravity: 5.9 – 6.1
Refractive index: 1.918 – 1.934; Uniaxial positive; 0.016
Luster: Vitreous to adamantine.
Dispersion: Medium
Dichroism: Strong.
Occurrence: Metamorphic, hydrothermal and pegmatites; Mexico, USA, Italy, UK.

Notes
May be dyed to look like many other stones; fine yellow may look like fancy diamond, but DR; also made synthetically; fluorescence: strong blue in short wave, but no reaction in long wave; may show didymium spectral lines in yellow and green; faceted for collectors.

Other People's Money

Memorable quotes from the movie:

Lawrence Garfield (Danny DeVito): This company is dead. I didn't kill it. Don't blame me. It was dead when I got here. It's too late for prayers. For even if the prayers were answered, and a miracle occurred, and the yen did this and the dollar did that and the infrastructure did the other thing, we would still be dead. You know why? Fiber optics. New technologies. Obsolescence. We're dead, all right. We're just not broke. And do you know the surest way to go broke? Keep getting an increasing share of a shrinking market. Down the tubes, slow but sure.

How To Grade Tea

Grading tea is an art than science + it owes its special effect to its caffeine, tannins, amino acid, protein content (s) + trace element (s): fluoride, potassium, calcium, manganese, vitamins: niacin, vitamin B1 and B2 + it acts directly on the brain and central nervous system (s) + it increases concentration.

Look how similar the concept is to diamond grading (old + new terms) + colored stone grading: it's either the color (due color causing trace elements), saturation or tone (based on percentage of elements + other modifiers) + other factors (like clarity + size, shape, proportion, symmetry, finish) that creates a unique gradation.

- Whole Leaf

- Flowery Orange Pekoe (FOP)

- Golden Flowery Orange Pekoe (GFOP)
- FOP with golden tips

- Tippy Golden Flowery Orange Pekoe (TGFOP)
- FOP with lots of golden tips

- Finest Tippy Golden Flowery Orange Pekoe (FTGFOP)
- Exceptional quality FOP

- Special Finest Tippy Golden Flowery Orange Pekoe (SFTGFOP)
- The very best FOP

- Orange Pekoe (OP)

- Pekoe (P)

- Flowery Pekoe (FP)

- Pekoe Souchong (PS)

- Souchong (S)

Experts may also add 1 to decribe top quality after leaf designation (s): like FTGFOP1, OP1, S1 and so on.

- Broken Leaf
- Broken Orange Pekoe (BOP), Golden Broken Orange Pekoe (GBOP), Flowery Broken Orange Pekoe (FBOP), Tippy Golden Broken Orange Pekoe (TGBOP), Golden Flowery Broken Orange Pekoe (GFBOP), Tippy Golden Flowery Broken Orange Pekoe (TGFBOP)

- Fannings
- Broken Orange Pekoe Fannings (BOPF)

- Dust
- Broken Orange Pekoe Dust (BPOD), Pekoe Dust (PD), Red Dust (RD), Super Red Dust (SRD), Fine Dust (FD), Super Fine Dust (SFD), Golden Dust (GD)

The grades of tea are represented by initials or a series of initials. Here are the grades of leaf sizes from largest to smallest:

- Whole Leaf
- Souchon
- FOP: Flowery Orange Pekoe
- OP: Orange Pekoe

- Broken Leaf
- P: Pekoe
- BOP: Broken Orange Pekoe

- Fannings and Dust
- F: Fannings
- D: Dust

- Additional Modifiers
- T: Tippy
- G: Golden

Usually they start at the lowest grade PS (Pekoe Souchong) to FOP (higher quality). They may also add modifiers such as GFOP (Golden Flowery Orange Pekoe) + even more modifiers such FTGFOP (Finest Tippy Golden Flowery Orange Pekoe) + SFTGFOP (Special Finest Tippy Golden Flowery Orange Pekoe) to improve the overall quality.

Beautiful Evidence

Good Books: (via Emergic) Beautiful Evidence is Edward Tufte's latest book. Tufte’s forte is information visualisation.

Here is what Wikipedia has to say about Edward Tufte:
Tufte's work is important in such fields as information design and visual literacy, which deal with the visual communication of information. He coined the term chartjunk to refer to useless, non-informative, or information-obscuring elements of information displays. Tufte's work argues strongly against the inclusion of any decoration in visual presentations of information and claims that ink should only be used to convey significant data and aid its interpretation.

The focus in this book is on evidence presentation. As Tufte writes in the introduction: (The book) is about how seeing turns into showing, how empirical observations turn into explanations and evidence, suggests new designs, and provides analytical tools for assessing the credibility of evidence presentations.

I believe the book makes you think about the meaning of words and images + the ability to interpret truth in simple language (s).

Multiple Personalities

Ann Landi writes about painter's experimentation in a variety of genres creating their own artistic personality + morphing narrative style (s) + other viewpoints @ http://artnews.com/issues/article.asp?art_id=2021

Nicky Oppenheimer Calls For African Mitigation Policies To Close Labor Cost Gap With India

Chaim Even-Zohar writes about the consequences of subsidies and/or two-tier pricing policies in diamond rough + De Beer's policy shift + journalist's dilema of reporting genuine news + other viewpoints @ http://www.idexonline.com/portal_FullEditorial.asp

Indicator Stones (Heavy Liquids)

In order to check the SG of the liquid, indicator stones are used. Indicator stones are small stones of a known SG that are kept in the bottles.

Heavy liquids and indicator stones
- 3.32: Methylene iodide: 100% = corundum (SG=4.00); jadeite (SG=3.34)
- 3.05: Methylene iodide: 68%; benzyl benzoate: 32% = tourmaline (SG=3.04-3.06)
- 2.85: Methylene iodide: 64%; benzyl benzoate: 36% = nephrite (SG=2.95)
- 2.67: Methylene iodide: 60%; benzyl benzoate: 40% = calcite (SG=2.71); syn.emerald flux (SG=2.66)
- 2.62: Methylene iodide: 59%; benzyl benzoate: 41% = crystalline quartz (SG=2.66); cryptocrystalline quartz (SG=2.60) Chalcedony
- 2.57: Methylene iodide: 58% benzyl benzoate: 42% = cryptocrystalline quartz (SG=2.60) Chalcedony; microcline feldspar (SG=2.56) Amazonite

These indicator stones are extremely valuable because they allow one to quickly estimate the density of the liquid. The number printed on the bottle is only a guideline regarding the liquid’s SG, and many factors such as evaporation or contamination can alter its SG. So it is of great importance that the tester checks the densities of the liquid daily. For instance, if you are using a 2.67 liquid and you find that calcite (2.71) floats very slowly, then the liquid must be slightly above 2.71. When a liquid’s SG does not exactly match the number of the bottle, it does not mean that the liquid needs to be adjusted. So long as you can find the SG of the liquid it can be used. This is the purpose of the indicator stones.

SG range of gemstones
When determining the specific gravity (SG) of a gem, one should always keep in mind that each gem has a plus or minus range of SG and not just a single figure. There are many factors which can affect the SG of a specimen, such as the clarity, inclusions, impurities, etc and a tester’s degree of error must be taken into account as well. So one can see that the final figure obtained is usually much less reliable than an R.I reading for instance. For this reason, it is usually not possible to separate one stone from another on the basis of SG alone unless their SG’s are apart from each other. You must always consider the plus or minus of a property. Although specific gravity is an important diagnostic property, in most cases, additional tests must be used to positively identity a particular stone.