Tools that may make your job easier
Part 2 of 7
By Mark T. Cartwright
A technique I learned more than a decade ago is generally termed ‘water grading’ and is practiced in at least two of the major laboratories. Its primary purpose is to make diamond clarity grading easier and more precise. I also use it (or a variation discussed later in this article) when examining coloured gemstones. The tools needed are easy to acquire and very inexpensive. I couldn’t imagine grading a diamond without using this technique—and I don’t!
You’ll need a small container with a relatively wide mouth and tight-fitting lid, distilled water, dishwashing liquid, and a sponge-tipped applicator. The latter can be found in most stores that sell makeup and are used for applying eye-shadow, lipstick, etc. They come in a variety of sizes, although I prefer the smallest. You can also purchase much more durable and professional-looking applicators from medical supply companies. These feature a 6-in. long handle with a sponge tip about an inch long. The longer handle and more extensive sponge make them very versatile for manipulating a loose diamond in tweezers or microscope stone holder. The makeup applicators each last for a week or so; the more expensive ‘professional’ applicators can last for at least a month with proper care.
To begin, simply fill the container about halfway (it really doesn’t matter if it’s more or less than that) with distilled water and add a drop or two of dishwashing liquid to act as a ‘wetting agent.’ Since diamonds are hygroscopic, the water beads up on the surface without the dishwashing liquid. If you add too much, you may end up with annoying little bubbles or a soap film on the stone’s surface; not enough, and the water’s surface tension won’t be sufficiently broken to prevent beading. Once the solution has been made, it’s simply a matter of wetting the sponge, drawing it gently across the container’s rim to remove excess liquid, and then ‘painting’ the stone’s surface while examining it under the microscope.
If you’ve never used this technique, I’m sure you’ll be startled by the view inside the diamond. It’s as though the stone’s surface disappears, along with any dust; the water seems to act as an auxiliary lens.
More to come of this story in Part 3.
Read the full article: A few of my favourite things