Monday, March 26, 2012

In Case You Were Wondering

About the copper red part.
It just occurred to me that some of you out there in Bloggerland probably don't know what the hell I'm talking about or know what the significance of copper red is.
So a little primer.
If you've been following along at home, you know that I dabble in ceramics and you've seen the goofiness that occurs from time to time.
Which reminds me, it's about time for more dabbling.
More on that later.
Anyways, the stuff I've been working with is mostly low fire clay, earthenware to be more precise, and is a different animal from what I used to work with which is high fire, or stoneware/porcelain.
The kiln being set up now is for high fire work, which vitrifies, or matures at about 2180 degrees Farenheit.
Low fire stuff doesn't vitrify and the maturing temperature varies although I work it at around 2000 degrees.
Give or take.
The most important difference is the ability to hold and absord water and the type of glazes used in the different firings.
High fire clay sort of turns back into like a rock, water absorbtion is very low, less than 1 percent while low fire remains porous.
Glaze color is also different as most bright colors burn off in the higher temps while most of the color spectrum is available in low fire.
Low fire:

Pure reds and yellows are very difficult to get with high fire.
I've only gotten a yellowish brown once, and I'm not sure how I got it.
Red, an oxblood red we call it, is difficult also but not impossible.
Well, it may seem impossible to some folks but all it takes it a lot of experimenting with glaze composition and kiln control.
High fire reds are created using copper and a touch of tin, usually in carbonate or oxide form hence copper red, and yellows with some variation of iron, either red iron oxide or some other impure form.
Variations in high fire red:

For scale, the taller bottle on the left is 18" tall.
The difference is that low fire red will come out exactly the same each time, while high fire copper red will vary with clay type and kiln firing.
High fire red, as you can see goes from dark blood red to a lighter almost liver brown red.
Actually I don't have any examples of the junk red for all of those got hammered and thrown in a dumpster.
I would say that out of maybe a hundred pieces of high fire red I've done, less than a third were kept intact.
I still got around ten of them.
The red glaze will not always burn red, you can also get white or a greenish blue. In fact I've got one pot sitting around here that shows all three colors:

That's the same glaze in the same firing.
In other words, getting a real nice copper red is sort of a hit or miss kind of thing.
Unless you work at getting consistant results.
Which I have tried to do.
Still anytime you do a copper red firing it's exciting for you never know what you're going to get until you open the kiln door.
In fact color consistancy varies so much, you never know what you are going to get in any color!
There are limitations in high fire though, like you'll never see a teapot like the above coming out of the high fire kiln.
If you look at the blue bottle in the second pic, if you squint yer eyeballs you'll see that the top portion, the neck is actually warped.
Things like bottles and teapot spouts and the like actually warp, unwind if you will, in the opposite direction of the wheel as they mature in the kiln.
I can't tell you the number of warped bowls I've had.
Not that I make a lot of bowls.
Anyways, for me copper red is a big thing, something I've worked hard at to well, I was going to say master, but no one gets a really firm grip on it.
All you can do is close the kiln door and hope for good results.
Which is something I did a lot of.
Hoping for good results I mean.


RANTWICK said...

I wish I was into something cool like that. My wife does lampwork beads and stuff, but that's just a little dinky kiln for annealing the glass.

I any case, I would ever have the required dexterity. Wishing you good luck with copper red.

RANTWICK said...

never have the dexterity, I meant.

rlove2bike said...

WOW...great work!! We dabbled a little with clay in high school. I wasn't very good at it.

Thanks for the post!

limom said...

RANTWICK, what I dig about clay is that you can work it in many ways, some of which require no dexterity at all.

rlove2bike, thanks!