Making permeable terracotta pots for sub-irrigation

Hi. I mentioned to a Mom-friend of mine, who is an awesome potter, about the irrigation we sometimes mention in permaculture using unglazed pots below the surface. Just a quick search gave me this link, for those who haven't heard of it.
http://www.arizonapottery.com/item.asp?iid=5759&pid=26&bid=5759

She's been very excited and made a handful of pots already, but they don't seep as much water as we were hoping. Our guess is that there's a special mix of clay (including some straw that's burned out?) or low firing that helps the pot remain especially porous. Does anyone have experience with making these pots and like to share details? I guess we could of course ask the folks at the above website, but since they're likely to view it as somewhat proprietary, I thought I'd ask here first.

Hi Kelda, I've been using a not so elegant but definitely effective DIY olla method. Check it out. The instructions are attached.

There is some info on it in this article...

http://permaculturenews.org/2010/09/16/ollas-unglazed-clay-pots-for-garden-irrigation/

this is the most intelligent thing to do! and save water!