Sham - I am interested in this neat bubbling problem you have.....

Could you try soaking the stone for an hour?

I think that would rule out the idea of the stone's porosity being the culprit if it still bubbles...


How about stopping by the grocery store and getting some distilled water?

This would rule out the idea of chemical reaction between something in the water and the stone.....


If both tests still bubble equally, then I would say that your stone must have air pockets in the matrix of the binder and it is simply being released as you hone...