Here is a real cone 6 gem...
25% Magnesium Carbonate
70% Nepheline Syenite
5% Kentucky Ball Clay (OM4)
This is the basic recipe of the crawl glaze that I've been playing with over the past few months. I found it buried in an old sketchbook scrawled in a corner of a page. It was from 8 or 9 years ago during a time when I didn't have any sort of studio access and was sucking up as much information as I could get my hands on. The recipe is attributed to a October 2000 Ceramics Monthly article on page 49, unfortunately I failed to note who the author was. (Hopefully someone can help me rectify that.)
This glaze is very temperamental and you need to place it in the kiln asap after dipping. The glaze will crack and begin to pull away but not quite fall... unless it's disturbed. It's very sensitive to thickness.The glaze will behave very differently based on what's under or over it.
Here's a link to a February post showing some of my experiments... http://fetishghost.blogspot.com/2009/02/test-yumoni-for-crawling-glaze.html
Experiment and have fun and please share any successes or failures you have.