I've been a dealer selling prospecting equipment since late 2006. In that time, I've had lots of people ask me about the Blue Bowl, and a recent conversation on the topic, got me thinking, "Why don't I just write this all down?"
So, here we are.
Classification
You can't talk about the Blue Bowl without first talking about classification and classifiers.
In my experience, most people get the wrong idea about classifiers. They go out prospecting for the first time and they're introduced to a classifier as a screen to get rid of bigger gravel and that's where their understanding sets itself in stone.
Classifiers screen off rocks.
But the root of "classifier" is "classify" which basically means to sort, in this case by particle size.
Most classifiers used in gold prospecting range from 2 to 100 mesh, but I've seen lab screens as high as 400. I don't work in a lab, so have no idea how high they actually go.
The number represents the number of openings in a linear inch, so the higher numbers represent smaller and smaller particle sizes. 2 means 2 per inch (4 per square inch). That means a 100-mesh classifier has 10,000 tiny holes per square inch.
Out in the field, you probably stick with a #2 or 4, but for the Blue Bowl, we're mainly looking at 30 minus. That's 30, 50, 70, and 100-mesh.
Your first job, before setting up your Blue Bowl, is classifying your concentrates. I use plastic mortar mixing tubs, one tub per classification. They're tough and cheap (under $8 at Home Depot).
Running Your Blue Bowl
First, stop staring at it.
That spiral of water is entrancing, and you will be drawn to it, but I swear it will give you a headache after a while, so don't stare.
The easiest setup is to run the bowl on a bucket in a tub. The pump sits in the tub pumping clean water. The bucket overflows back to the tub and recirculates.
The big idea here is that the sand stays in the bucket.
Go ahead and buy the Blue Bowl leg levelers. I was a holdout at first, but that bowl will try to shift around otherwise, and you want it both level and stable.
Now for the secret sauce. Slow everything down. Impatience is your enemy with a Blue Bowl.
Feed material slowly and take time after every adjustment you make to the flow.
The inlet has a valve to control the flow of water, and what most people don't realize is that it takes time for each adjustment to reach the center of the bowl.
You turn up the flow and nothing happens. Up again, and nothing. Up one more time and then whoosh, all your adjustments finally reach the center of the bowl and everything washes out.
Be patient. Go slow. Adjust and then wait.
Run one size at a time, cleaning up in between. Disconnect the pump during cleanup to avoid creating odd currents.
And that's it.