I also put this image in my original post. This is a small sphere of rose quartz being roughed in with my marble machine, which needs a new motor. I am in the process of building about a 15" machine which will replace it. You can see the three grinding cups, which are standard steel plumbing parts. Copper would be better. The abrasive is 60 grit diamond mixed with kitty litter. As more rocks are ground up it will turn more muddy brown and eventually you will have to pan off the excess clay with a gold pan leaving pure diamond and start the grit bath over again.
Regarding the panning method of diamond seperation: I'm not sure if this is helpful or not but I occasionally separate various sizes of crunched up sandstone (for someone who's wanting to do sand paintings - I find the stone in many colors). Here's the method I use - gets rid of matrix, mud etc and allows separation into at least two or three grit sizes.
a.) At least six large cylindrical glass vases (as tall as you can fit under a sink to fill) - about .99 cents/ea at goodwill.
b.) 5 gallon bucket.
c.) A long enough spoon to stir material in the vases of the sizes you've acquired. Three spoons are better but one can be used and rinsed between stages.
d.) Stopwatch. If your wrist watch has one then you're set.
2. Line your vases up in course to fine order with the bucket in the middle area so you can pour from any of them easily into it.
3.) Fill the first vase 1/4 with the material to separate and one half to two thirds of the rest with water.
4.) Using your stir spoon, stir the contents of the vase until you get a nice vortex in the middle going. It's easiest on the vases if you do this by always stirring just above the material settled on the bottom rather than in it. Especially if you're doing diamond as even sand scrapes up the bottom pretty good and pretty quickly - I can only imagine diamond...
5.) Stop stirring, quickly set the vase down and hit the stopwatch.
6.) Watch carefully (you might want to use a flashlight for muddy water - illuminate from the front, not the back - refraction can throw you (it does me anyway - tiny bubbles and tiny grains can look the same in some light).
7.) When only the most course material you want to keep has settled, note exactly how long that took.
8.) Stir again, set down and hit the timer. About 4 or 5 seconds before the time you noted is up, grab the vase and pour the contents very quickly (quickly
all the way down until there is very little water left over the settled material) into the second (medium grit) vase.
9.) Repeat steps 4-9 for vase 2, seeking medium grit.
10.) Repeat step 8 for medium grit, pouring contents into vase 3.
11.) Now repeat steps 4-9 for vase 3, seeking the rest of the material you want to keep (you'll lose some of the finest unless you want to be there all day getting it mud free - maybe you do, that's fine too).
12.) Repeat step 8 for fine grit but this time pour the leftover waste into the bucket.
13. When the bucket is full empty it somewhere safe (clay down the drain - bad idea unless you have a really good clay-trap).
14. Add water to the contents of vase 1 and repeat the stir/pour steps for each vase using the noted settling times. Do this until the water is clear enough that it can be used. Totally clearing the water, I'm afraid, takes a lot of water and a long time. Perhaps you can use this with panning of the finals to more easily get them cleaner. I should think, however, that this would leave you with well usable material and rid you of a great deal of super-fine muck pretty quickly.
15.) Once acceptably clear, fill each vase 2/3rds full with water over the materials, stir vigorously and immediately pour into the three remaining vases (one for each grit) to gather most of the materials.
16.) Add more starting material to vase 1 and repeat the entire process to step 14.
17.) Gently drain the excess water from your three final retaining vases before adding more to them by repeating step 15.
This is all pretty intuitive and while it works well for me it may not work, or one mind it 'sucks', for everyone. It's kind of labor intensive but more so in an aerobic way than a heavy lifting way.
The main advantage I can think of would be separation of grits. You can do this all with just two vases if you don't need separation of grits - that is, if you're just after all grits below a given size or all grits as mud free as possible.
A secondary advantage is that if you don't require super fine grits then you will probably be able to get the water pretty clear pretty quickly and with minimal repetitions.