Iron Micro Structure

Welcome to your Iron Micro structure walk through...



First Step: Identify the Iron. It all starts with this little "slug"
Lets say that we are in a Laboratory and we happen upon a little piece of iron that looks like this...
How to identify?
-Normal circumstances would tell you what kind of iron it was with some sort of sample ID
EX 03222023222202 would tell us the sample was today at 1020PM and it is a ductile iron of the 2202 grade...which basically tells us the hardness range we are looking for.
However that is hardly enough...we must uncover more about this little slug.


Second Step: Hardness

If you are lucky your lab will have a camera used specifically for checking hardness.
Check for calibration...there should be a block around labeled with the correct measurement.



Intermediate Step:
POLISH that surface until it appears like a mirror and then give it an etch.







Step 4: Examine under the microscope

After a proper polish under 100X the surface should appear something like this....

The nodularity of the second photo is much better. So a good polish is key to a good sample.

Better polish...worse picture.

poor polish however nodules still present

Gray Iron

Grey Iron has a few major differences than ductile

First the chemistry
gray iron has more of the following elements
-manganese
-Sulfur (bonded with pyrite)
-Silicon
-Chrome

Grey Iron

...hmmm
Less Carbon
....and
a dash of titanium

Polished up it looks like this



In a foundry gray iron gets poured much faster than the ductile iron because it can be melted faster and it needs less additions before it gets poured into a cast



As you can clearly see there are no nodules present. The addition of magnesium right before the iron gets poured forces the iron to form into nodules. This makes the iron much stronger in tensile and hardness aspects.
Gray iron is much better for absorbing and redistributing heat...so it still has plenty of uses.

Tanzanite - Azotic Coating and D - Block Origin

 
The D Block term was used because the best tanzanite supposedly came from that dig.
Actually, wherever they hit the seam, they got great material. I can remember when the smallest piece I could get was over 10 cts., with trays of 20 ct. + material, huge rounds looking like acorns with the deep pavilions they cut them in. The costs then would still easily give you your keystone profit now, despite a 20% drop in value from its highest price.
Azotic coating will give you greater color saturation at the edges than the center, opposite what an untreated gem does.
Under a microscope, put the gem in the cut off bottom of a dixie cup with water just up to the girdle. The difference from eye-balling it will be stunning.
The "blue-green tanzanite, untreated" piece I tested was colorless, table down in the water. I turned it over and the color showed only on the facets above the girdle and the table was still colorless.
If you see any tubules of color filling inclusions, it has been lattice diffused. This process can take colorless rough and subject it to enough heat and pressure that introducing gaseous metals causes the rough to take on color. Crap material to gem material in the lab. A flood of no reserve bids, consistent color saturation and larger gems on e-bay from vendors who are power sellers you never heard of before is a dead give away. That's the deal with all this blue-green tanzanite; cheap because a lab used azotic coating to get color where there was none.
1 ct., emerald cut, VS and $9.99 to open and there's so much, mine was the only bid.
Please. Chinese vendors have pages of something the knowledgeable know was hard to come by and never cheap, but it sells and degrades the industry with every false sale of "untreated" gems.
Some of the faux material was even touted as "D block" origin. Insult to injury. 

It sounds like the standard immersion cell examination will reveal that classic color saturation near the facet junctions. I have not seen any lattice diffused goods yet (other than in the GIA NYC LAB), but I know they are out there in quantity. Hope the immersion exam will show that as well...

some coated stones will show a weird iridescence across the PAVILION when you rock/roll it under a light source -- especially some of the coated beryl/topaz/quartz materials, but also when examining stones such as fancy-color DIAMOND. Some it shows up better in diffused light, but some find it easier to see when viewed under more focused light, moving the light around the surface of the stone.