Version 6 Asha in production...
Asha's version 6 production process is now registered with a US Patent:
U.S. Patent Application No. 12/139,931 -- Method for Producing a Highly Refractive Composite Gemstone, and Product
Asha® is now only being made in version 6, and all Asha's are by default version 6.
The difference - for version 6, we introduce an 'optical layer' that is put on the core, and that is then sealed in with our traditional high-purity amorphous diamond.
The optical layer is a proprietary compound that has a refractive index of 2.5, greater than natural diamond whose refractive index is 2.42. Thus the optical layer boosts the light handling ability of the version 6 Asha, increasing the luster and sparkle.
The improvement can readily be shown by analyzing refractive indexes using a digital refractometer.
Plain CZ = 2.165 RI
Asha v5 = 2.183 RI
Asha v6 = 2.20-2.24 RI (note, due to it being a composite product, its RI varies from spot to spot).
Here is a photo of an Asha v6 in the digital refractometer:
Both versions use an amorphous diamond infusion process, so the outer surface of the finished Asha is identical, with all the benefits that the amorphous diamond provides (seals and prevents the normal clouding reaction that CZ has with air and water, keeps the Asha cleaner longer, reduces the 'blue haze' and glassiness apparent with most plain CZ, etc).
The optical layer is created and applied at a high temperature, and as a result, in induces some 'feathering' to the CZ core. Version 6 Asha's thus are not internally flawless like version 5, but rather are VS grade on average. The benefit is that each stone has unique defects, making it easier to identify 'your Asha' should you give it to a jeweler for mounting and be concerned about not receiving the same stone back.
The main difference visually is that version 6 has a slightly higher luster and a bit more sparkle, due to the addition of the optical layer.
As noted, version 6 is the only version BetterThanDiamond has been making, since July, 2008.