I got them from Woodstone a few years ago. As part of my business I specify their ovens when appropriate. I don't sell them or anything, but I do specify them. (I'm to a kitchen as an architect is to a building ... a designer.)
Woodstone makes their hearths (4" to 6" thick, depending on the oven size) by pouring a ceramic slurry into a mold. This must be done in a single pour, so they always make a little more slurry than they actually need to fill the mold. They pour the remaining slurry into half size commercial sheet pans and were in the habit of giving them away to various people .... like us designers .... their sales people .... customers, etc. etc. (In fact, if you look closely at the picture, above, you can see that one of my stones is still in the sheet pan ..... it stuck and couldn't be "unmolded".) Anyway, that's how I got mine.
I understand now that they're selling them as pizza stones. That said, there's no mention of them on their web site. I also understand that the ones the size of mine are supposed to have an MSRP of $125.
The stone itself is made, as I said, from their proprietary hearth material. It is very dense and formulated specifically to gather and retain heat. In my experience, they do what they're supposed to do. In home use, mine has never failed to make a great pizza. After pizza, after pizza. They don't lose as much heat, as a percentage, to the product as do other stones. In other words, they have much more thermal mass, and thermal mass, in a hearth oven, is where its at. That ... and radiant heat.
I have experience with the typical pizza stone sold at stores in the $20 range. These are made from a far more porous and lightweight material. They tend to draw moisture from the dough. That's not a bad thing, but it is a different principle than the imparting of heat, which these stones do. These stones are not at all porous. Rather than draw off moisture by wicking it into the stone and vaporizing it from there, these "boil" it off on the surface. A small difference, but different, to be sure. The bigger difference is in the thermal mass. The lighter stones just don't have the same thermal mass.
Does the use of two stones make a difference? I think it does. The lower one replicates a true hearth. The upper one replicates the (nearly as essential) oven dome. In a true hearth (black or white) oven both the hearth and the dome play vital roles in the cooking and baking process.
These are sold to do essentially the same thing:
Here's a web site that has them. Click on the picture to get a better understanding of what they are and how they work. I have no experience with these gizmos, and have never seen one except of the web, but they look pretty interesting.
http://asp1.walkontheweb.com/hearthkitchen/store.aspI would also suggest you go to Woodstone's site and read their dissertation on oven history. It puts some of this "science" into a more practical perspective. You might also google "hearth oven" or similar terms. There's lots of info out there on how a black or white oven works. (Black oven - fire built within the oven itself. White oven - fire built in a separate chamber below or beside the cooking chamber) These ovens date to man's earliest days and the science of them has changed very little over the thousands and thousands of years we've used them. Just the materials and construction techniques. But the basic science of them ..... virtually identical.
For what its worth, I'm in the early planning stages of building a brick dome oven in my back yard. Will it ever get built .... :shrug: But the whole idea really fascinates me. There's another person who has occasionally posted here who has built one. Here's a thread that talks about ovens. Look down the thread for the post and pictures from the poster Willy Lee.
http://www.democraticunderground.com/discuss/duboard.php?az=show_topic&forum=236&topic_id=3501Il pane - il personale di vita (Bread - the staff of life)