Color: H Color or better. Cushion cuts are one of the worst shapes when it comes to retaining color (or one of the best, if you’re a manufacturer of fancy color diamonds).
This is why you find that Cushions and Radiants are the two most common shapes in the fancy color diamond market. For this reason, I recommend my readers stick with H or better when buying a cushion cut, unless it will be set in yellow gold (in which case, you can go down to J or K)
Clarity: Stick to SI2 clarity or SI1 clarity for the best value. Since cushion cuts have a large open table, it might be difficult to find a nice eye clean SI2. So you might have to compromise and end up paying a bit extra for a higher clarity stone.
Don’t trust a site listing virtual inventory at their word regarding checks for eye-cleanliness. Only use a vendor that offers high quality photos and only trust their eye cleanliness check if they’re checking it themselves.
Cut Parameters for Cushion Cut Diamonds:
Depth: Under 70%
Table: Under 70%
Polish/Symmetry: Good, Very Good, or Excellent
Length/Width Ratio: Whatever you like!
As you can see, these parameters are very loose. It’s important to remember that with Cushion cuts (as is the case with many other soft-sided fancy shapes), you can’t really evaluate a stone’s cut quality by its numbers alone.You need to see the stone and see with your own eyes how it looks.