Slurry PH?

Interesting.

I never have trouble with gassing, always actually pulling a vacuum inside my barrel.

I am tumbling Agate Creek Queensland Australia Agates almost exclusively.

Some of the Agates I collect have Calcite and/or Aragonite inside vuggs, some have Agate pseudomorphs after Calcite or Aragonite, some have yellow flecks of Calcite (presumably) included that make the Agates fluoresce under UV. So presumably the rock is basic. I don't tumble the Calcite if I can help it.
The water I use is country rainwater.

I am tumbling in a steel LP gas tank. A 4.5Kg tank.

I have tumbled in a highly caustic slurry by adding Caustic Soda.
My thinking was that the caustic might help the slipperyness of the slurry, chemically remove some Agate edges and dissolve rock powder out allowing more contact with Silicon carbide grit.

It worked to a certain extent, I'm not sure that it did much of anything to the actual rocks, but it certainly dissolved the rock powder from the slurry.
I didn't keep it going as it was just too dangerous working with a highly caustic slurry plus if you let the slurry dry out exposed to the air it would absorb Carbon dioxide and the Sodium Silicate would harden to a brick.

I might have to try adding a bit of acid to one of my plastic barrels. Prepare for barrel explosions I guess.

I too notice a vacuum on my barrels. Cold day fill/seal hot day clean out. Still the lid is sucked on.

No explanation. Just observation.

I'm using tap water, kitty litter clay and silica rocks. Never borax.

I still don't have polished stuff........

Sorry not much help.....

The chemical depositions that move silica and calcite occur on over a much longer period of time than the mechanical forming occurring in tumbler barrels. I would tend to use a chemical that would aid in the removal of material, much like what pauls did.

Having dealt with acid and caustic reactions to my flesh as a young man, I am good with the hard water around here.

Your skin is quite an effective protector against pH extremes, breaks in your skin is where the problem is.

I get more vacuums than positive pressure Scott.

ph has to play a big role in gas build up in a sealed rotary barrel.
If you have ever tumbled concrete you will find the slurry is very alkaline. Even if you add just 20% concrete chunks mixed with agate.
That 20% concrete will often create pressure in a sealed rotary. Concrete chunks are like adding alkaline pills to the mix.

Tumbling brass, copper and stainless steel also creates positive gas pressure(in my case). My water is ph 6.

One solution to tumbling high gas materials is simply using a slant rotary tumbler where the contents do not need to be sealed.

That process could be used to fill pits and heal fractures in agate slabs!

Hard limestone can be variable depending on silicification. I suppose some real hard cherts are silicified limestone.
I would not think ph is going to effect the abrading process. Abrasion being totally mechanical. Or supposed to be.
Muriatic acid will sure eat the some limestone pockets out of agate. But that is some serious acid. Certainly no one is going to tumble rocks in it.

Mud in one end, three hours @1500 degrees later,
out comes the nice uniform pebbles.

Interesting Chemistry as a Lime Kiln Operator.

Let the mechanics do the work ? YES. It is complicated enough without involving chemistry.
Unfortunately the rock does grind into particles perfect for reactions. Not much can be done about that.
No telling what kind of brews have been amalgamated in the ole rotary.

i know that my coral and Rio agates-jaspers-and pet wood makes a plant friendly slurry.

As far as the coral's high limestone content I would assume it is the lime added at a near chelated state from the fine grinds. Ag lime.
Ag lime is faster acting as it is finer. 1 inch pebbles take a long long time to raise ph of soil. ag lime is normally 30-90 mesh, it varies.

For maintaining a healthy pasture in most of the east 1 to 4 tons of Ag lime is spread every 3 to 5 years per acre.