You can find cutting instructions for the updated Rainbow here.
A New and Improved Rainbow
Faceters often tell me they have the most trouble with my original Rainbow gem design. It can be difficult to cut, especially for those with low mileage. So, I’ve reworked the original to make it better and easier. However, this is still not an easy design. I don’t especially recommend it for novices. All the same, it’s definitely easier than the original.
This Rainbow version performs better in lower refractive index (RI) materials. I set it up particularly for 1.62, such as tourmaline and topaz. You can cut it in RIs from 1.62 to 2.14 with no changes. For quartz, add 0.3 degrees to all the pavilion tiers (40.5 degrees).
You can end up very easily with the wrong L/W on Omni point Barions. Therefore, a preform of the correct L/W is always helpful. If your breaks look like the Rocky Mountains, check your L/W. It’s probably off one way or another.
Notes on my Rainbow-Cut Malaya Garnet
The garnet pictured here started out as a really awful native cut. I needed to design something that would give me a decent weight return and still get some life into this huge red garnet I’d purchased. So, I decided I needed a brilliant pavilion, even if the rough loss was going to be higher (and it sure was).
Enjoy cutting your own updated Rainbow.
Detailed faceting instructions by Jeff Graham available at The Rock Peddler