As far as the red earthenware goes, the redart recipe doesnâ€™t look like it has a lot flux in it, so I would think that it is porous like other red earthenware. I wonder how much flexibility does play a role, he did mention a cone 1 firing didnâ€™t make it stronger, which I assume means it was just as strong. Could the high iron content of red clays have something to do with the results?
About difference between cone 6 porcelain and 10, from what I have read there are more and longer mullite crystals at higher temperatures, it would be nice to know how much of a difference it makes. Here is an interesting paper on the subject that seems relevant.... Mullite development
It would be interesting to compare a vitrified 6 and 10, under glazes with similar compression (or how ever you would do a fair comparison), then put them through a series of tests. Until then, I'll rely on everyoneâ€™s real life experience, because I only fire to 6. I'm really only curious though, cone 6 has proven to be strong and durable enough for my needs.
On a similar subject, Matt and Daveâ€™s clays have published results on there website in the science section, showing how a cone 6 gloss glaze, using the right amount of boron, can be more durable than a 10.
I guess I do everything-breaking the rules. 1)I set up my cone back so that it sets parallel to the peep hole, perpendicular to the wall. 2) the cones are set at opposite angles along the length of the coil of clay. 3) I set the cone very close to the peep hole so that I can see each cone when loading the kiln. 4) I pack a kiln way to tight to see an element on the other side of the kiln.
Thank you for the alternative info, important points.