Posted 04 June 2008 - 10:00 AM
The advantage of the blue bowl is that it gets just about everything as long as you pre-classify, make certain that the blue bowl is absolutely dead level, pay attention and make timely adjustments to the water velocity. This is labor intensive, but also is the most efficient and a very gratifying way to capture virtually all of the very smallest gold. If you are not careful and allow the water velocity to gain too much momentum, you will loose some of your gold -- especially if you are running the very smallest gold in the sub 100 range. The reason the water velocity changes is because the mass of concentrates that you start a run with gradually diminishes over time. The water will pick up speed as it has less mass to restrain it. You will be able to see this by watching the water level rise inside the blue bowl. Thus, for example, if you begin the process with the water level a half inch below the top lip of the bowl and a cup or so of black sand spread evenly across the bottom of the bowl, as the concentrates are carried up and over the vortex hole they form an octopus looking pattern of black sand bars at the bottom of your blue bowl and as these bars diminish in size the water level will inch higher upward and the velocity will increase accordingly. To control this acceleration, you can install a relief valve to bleed off water volume from the inlet. I accomplish this with my blue bowl by employing a cheap, plastic garden hose "Y" splitter. A hose from the bilge pump screws into the bottom of the "Y" splitter. The main power lead from the "Y" goes to the inlet of the blue bowl. The other has a short bib hose attached and leads back down into the tub that contains the water and the bilge pump that powers the whole thing. The "Y" splitter has an adjustable valve on each outlet. Thus, I can fine tune the water velocity without creating excessive back pressure on my bilge pump. A side benefit is that I can utilize the bib hose to flush off the grit and dust-like particles that accumulate on the nylon stocking that protects my bilge pump. By doing so I seem to get longer battery life. Note, also, that as battery voltage diminishes so does the output of your pump. This is where the "Y" splitter also helps. By cutting back on the volume of by-pass water, I can maintain sufficient water velocity inside the blue bowl even though my battery is dying. You will not believe the amount of fine gold you will end up with at the end of a run. To rapidly remove this virtually pure gold from the blue bowl without messing up the exact level that you worked so hard to establish, shut off your pump and just use a plastic pipette to "blow" all the fine gold into one edge of the bowl. Then simply suck it all out with the same pipette (or a larger one such as a snuffer bottle) and immediately transfer it into a vial. Now the blue bowl is ready for another run. Just dump another cup of black sand into the bottom and smooth out. Then turn on the bilge pump and start emptying another long neck. Helluva great way to spend an afternoon.
The spiral wheels process much greater volumes than the blue bowl, but they are not anywhere near as efficient. They, too, require fairly close attention, at least for initial set-up to establish the correct angle. I still own one -- the type that can be run either wet or dry. But for the most part I do not find them to be very useful because an even greater volume can be processed much more quickly with a recirculating sluice or just by simple panning. I gave away or sold all my other models some time ago. However, for those that do not possess sufficient panning skills or do not have a recirculating sluice, this might be an option to consider. Especially if you also are interested in recovering gem stones. Hope this helps. Good luck!
Prospecting success, be it for HEARTS, TRUTH or GOLD, takes COURAGE and HONESTY to penetrate through the appearance of things, plus PATIENCE and FORTITUDE to work through the many layers of things of which both nature and human nature are composed.