Those tend to be very porous and probably won't take to the acid stain so well. They're made of concrete, but it's not the same mix, these are dryer, therefore more crumbly. Poured concrete (the fake stones, counters, floors, statues, etc) is a different mix so it has a smoother 'shell'. That shell is etched with the acid and the color adheres.

I've not tried to acid wash this type of concrete product but, you could try one and see if you like that. To get an idea just try diluting some water based wood stain, brush it on, then let dry. If you like the effect, try acid stain. Or, you can just leave the wood stain and put a clear sealer on it if you want the color to stay. It's easy to reapply later, tho.

I'm the wife of a decorative concrete guy...so I get to see all his experiments with concrete coloring. He's been using this new stain that he mixes with the muriatic acid that looks like rust. It's really cool, and I'm considering trying it out on the stone fence I have in the back yard.

Thanks for replying Pesky --

I know they're very porous and would have a completely different look, but thought it might be a 'good' look, even if it's different.

Trying with wood stain could give us an idea, though I would imagine the durability would be very different. Would we still get a 'marbling' effect? Or maybe one of the color test kits?