Wednesday, April 8, 2009

stoke hole plugs 2.0

Here are the new stoke hole plugs (along with a couple of larger pots that still have a lot of drying to do). I decided to keep the same shape as last time. The clay is incredibly groggy (well groggy, and "saw dusty")when compared to the last batch, so I'm hoping they won't warp much at all.
As for the recipe I ended up slaking down forty pounds of the old clay (50/50 EPK kyanite) then added ten more pounds of EPK (we didn't have any fire clay at the studio.... go figure) along with ten pounds of coarse grog. I then tried to estimate out and add one third sawdust by volume. After this mix dried enough to use I found it pretty lacking in plasticity, to the point I was having trouble just keeping together to wedge. So I added a little bit of wet sagger clay from last cycle, maybe about a third. So the math gets a little fuzzy and convoluted, but as far as I figure the end recipe looks something like this:
43 EPK
33 Kyanite
10 Grog
add 2/9ths sawdust by volume.

We'll see how this works. I can tell you one thing though, it's a little painful to throw. I ended up pounding the lump of "clay" into a ring with a flat base instead of opening it, then centering and throwing exclusively with a sponge in one hand and a rib in the other (using almost no water as per Alex's suggestion). Hopefully it will work well.
You can also see in the picture I used a little bit of the clay to make a plug for our blow hole in the first chamber (which we cast into the key using a plastic cup. Our first firing we left this open while firing the second chamber and ended up cooling the first chamber a little more quickly than we would have liked (we also had a little bit of dunting from pots underneath the blow hole). So we'll certainly close it up tight this time around.
that's all for now, just finishing up some pots and trying to figure out what needs to be done as far as kiln prep goes.


Alex Solla said...

I had another idea for your stoke hole dilemma.... what about taking 3-4 softbricks, mortaring them together with greenpatch or something similar, then essentially trimming away the form till you have a round brick? Start off by cutting the main corners with a hacksaw or bowsaw, then attach it to the wheel and trim with either an old trim tool or even a hard brick. Then you could just dip the whole plug into either kiln wash or ITC. I think then you'd have a lighter plug that would be MUCH more thermal shock resistant.

Looking forward to hearing how your latest ones hold up.


Michael Kline said...

I tried the "glued-together-soft-bricks" and eventually, before the first firing was over, a couple of them had already come apart. Maybe if you dipped them in satanite or equivalent, and bisque fired them?

I've heard of others who had the same thing happen. I've never had trouble with my plugs breaking from thermal shock; hot:cold. Of course I'm not using mine for the stoke doors and are handled a lot less than a stoke door.

I'm partial to the hand-made look of your plugs. Anyway, how cool is that to have a handle on your spy plug. Here's my post from a while back about my plugs.

But what I really wanted to say in this comment was how I covet those saw horses!!

Joe and Christy said...

Hey guys,
I'm feeling pretty good about this round of stoke hole plugs. If they don't work though I was thinking that I still have the plastic planters that I used for casting the stoke holes in the kiln. I could take some plaster casts of these and give a try at some kind of stoke hole plug press. Press them with as little water as possible.
Michael, it certainly is nice to have some saw horses to set where ever you need them to dry pots on or whatever else. You're a handy guy though... they aren't hard to build.

Michael Kline said...

Joe, I have a couple sets of saw horses around, but nothing as nice as yours. Also around here, in the mountains I make a couple of legs a little longer than the others. ;-)