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My search for the perfectly cut asscher has led me to a lab grown stone

diamondhoarder

Brilliant_Rock
Premium
Joined
Apr 5, 2012
Messages
648
@diamondhoarder Since you're returning the diamond, I'll chime in with a conjecture as to why you find it so unexceptional: the diamond has pronounced strain which negatively hampers the light performance of the diamond.

In the video you posted you can clearly see the strain lines running from 10 o'clock toward 4 o'clock (top left to lower right). The strain is caused by dislocations in the the crystal lattice.

When the light hits these dislocations it causes the light to split (birefringence is the technical term) and it simply results in fuzzy, mediocre light performance when the diamond is not blasted with light in a lightbox.

All diamonds (mined and man-made) have strain in the crystal; however, CVD diamonds can have much worse strain (and worse light performance) than mined diamonds if the seeds are of poor quality, or disadvantaged CVD reactors are used to grow the diamonds.

Personally, Asschers are my favorite cut and my first impression of your chosen stone was quite positive (similar assessment to you), but once I saw the stain in the video I would have immediately rejected the stone for the same reasons you chose to return the stone.

The last time I checked 0.37% of lab diamonds offered to us were Asschers, so finding a good one is quite difficult. All the best with your search!
That's really interesting, and not something that I noticed. I have never heard of strain before - is this different to striation? I did notice some slight unusual texture when viewing the back of the stone on the video, although I was unsure if that was a polish issue or possible striation. Your explanation would certainly explain why the stone was a let-down despite its promising specs. I clearly have a lot to learn about lab diamonds!

@Ada Diamonds CEO Thanks for your very interesting post about strain. As you can see from the subsequent comments people are interested to learn more. Could you answer a few of our questions please if you have a minute? Is strain the same as striation?
 

Lessics

Brilliant_Rock
Joined
Jan 6, 2019
Messages
581
So interesting. I have read somewhere that all MMD have some internal graining. Is that what "strain" means? In some situations the internal graining will affect how the diamond looks, and in others not so much. This is one of my concerns going with MMD. I used to own a MRB that had internal graining, and it didn't affect how it looked. It just bothered me when I saw it under a loupe.
Only CVD grown diamonds have a risk for striation issues. HPHT grown diamonds have a risk of blue nuance. But both growing methods can produce beautifuly cultured diamonds. Just like there is mined diamonds with internal graining or undesirable tint.
 

LLJsmom

Super_Ideal_Rock
Premium
Joined
Oct 24, 2012
Messages
10,022
Only CVD grown diamonds have a risk for striation issues. HPHT grown diamonds have a risk of blue nuance. But both growing methods can produce beautifuly cultured diamonds. Just like there is mined diamonds with internal graining or undesirable tint.
Thank you. That is good to know.
 

Lessics

Brilliant_Rock
Joined
Jan 6, 2019
Messages
581
Thank you. That is good to know.
Of course! It took me a few weeks/ months to sift through all the MMD information and what one needs to be aware when purchasing an MMD.
CVD diamonds are grown in “diamond layers”, like snow falling on a snowman. HPHT diamonds are grown with pressure like mined diamonds. A blue tint in a HPHT diamond comes from too many boron elements. This happens when the diamonds growing is sped up (that’s what I read). That’s why HPHT grown diamonds are often classified as Type 2b. Even if a HPHT grown diamond is a type 2b on its cert it still can have no tint. Most certainly now state if a diamond has a blue tint. These diamonds are also priced accordingly.
 

Ada Diamonds CEO

Rough_Rock
Trade
Joined
Jan 8, 2020
Messages
69
@Ada Diamonds CEO Thanks for your very interesting post about strain. As you can see from the subsequent comments people are interested to learn more. Could you answer a few of our questions please if you have a minute? Is strain the same as striation?
I'll try to carve out some time this weekend to go deeper on strain and striation in CVD diamonds.

Strain is not the same as striation.

Striation is due to a couple of things:
  1. The stopping and restarting of the diamond growth process, which results in distinct layers in the diamond like rings in a tree.
  2. Momentary disruptions to the plasma at the surface of the diamond, which can cause concentrations of atomic defects in the diamond.
Some growers need to stop the growth every 0.5mm, better growers can grow large crystals suitable for 2-3ct gemstones in one single growth cycle (meaning there will be no striations in the diamond).

Striations can cause strain in the diamond, but the primary source of strain in a CVD diamond is often the defects in the surface of the seed used to grow the diamond.
 

OoohShiny

Ideal_Rock
Premium
Joined
Apr 25, 2014
Messages
8,191
I'll try to carve out some time this weekend to go deeper on strain and striation in CVD diamonds.

Strain is not the same as striation.

Striation is due to a couple of things:
  1. The stopping and restarting of the diamond growth process, which results in distinct layers in the diamond like rings in a tree.
  2. Momentary disruptions to the plasma at the surface of the diamond, which can cause concentrations of atomic defects in the diamond.
Some growers need to stop the growth every 0.5mm, better growers can grow large crystals suitable for 2-3ct gemstones in one single growth cycle (meaning there will be no striations in the diamond).

Striations can cause strain in the diamond, but the primary source of strain in a CVD diamond is often the defects in the surface of the seed used to grow the diamond.
It would be cool to know which growers supply which vendors, but I imagine all that sort of thing is very much 'trade secret'.

Personally, I'd quite fancy a blue nuance stone, even though the grading houses have been pressured into no longer mentioning it on grading reports :rolleyes: but then I'd fancy one of the ultra-pure stones that John Pollard has previously mentioned, where they seem to be something like a 'C' colour!
 
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