Wednesday, September 28, 2011

Unexpected Results

If you can picture it at home, I have the ability to raise only one eyebrow at a time, sort of like Spock in the old Star Trek:

I don't say fascinating or anything like that, but when I took a look at what happened in the kiln last night, I had to raise an eyebrow.
First of all, to take care of some questions, glazes are formulated to reach maturity at different temperatures.
On the other hand, most have a temperature range of about two cones, or 80 degrees F give or take.
The maturing range depends on what's in the glaze chemically, and the flux differs in the glazes I'm using now, and the glazes I used to use.
Specialty glazes on the other hand again, are well, special, so they tend to have a range all their own as we shall see.
Without getting all technical(and it's not as technical as it sounds, okay, it sort of is) the glazes I used on the Teathingy No.3(working title) are specialty glazes of sorts and are supposed to be fired two cones hotter, again about 80 degrees, than the regular glazes I use.
These specialty glazes are metallic so I'm supposing there's something in them that need the hotter temps.
If I could see the formula I might be able to figure them out, but seeing as how they are commercial glazes, the formulas are not available.
Okay, some glaze goofiness.
First firing and second firing:

As you can see, the second firing turned the glaze a dark dry matte compared to the first firing, which was at the correct temperature, which sort of created a metallic gloss.
The brass glaze held up sort of okay, but the lid did lose some shinyness and looks more distressed than before:

So what happened?
The second firing was done at a lower temperature, for the treads and wheels were done with a different glaze, a satin black.
I didn't want to over fire that glaze, for usually the results are not good when you over fire and well, the glaze is sort of a permanent thing.
In the second firing, I'm thinking the metallic glazes sintered(fluxed), but not enough to gloss over hence the dry matte look.
In other words, the metallic glazes were under fired.
Make sense?
Because I'm using three glazes that fire to two different temperatures, I either over cook one, or under cook the other.
I was actually hoping that the hotter glaze would hold it's finish, because it's a hotter glaze, but apparently that didn't happen.
Typically, when using different glazes, you would fire the hottest first, then the lower temperature ones because once a glaze is set, a lower temp usually won't alter it.
So what to do?
I can refire again, this time to the hotter cone in hopes the metallic glaze fully matures and regains the gloss, and the cooler glaze doesn't over cook, or I can just live with the results.
Which in my opinion, aren't that bad.
Except it's really close to the finish I got the Industrial Teapot, and well, I'm not real happy about that:

There's another before and after.
I actually like the second one better, but again, I wasn't looking for something that was like the other thingy I did.
I have time to do a test on the lower firing glaze, to see if it will take the higher temps, so I may refire one more time and try to get the original finish.
Or I may not.
So in response to your questions, you can "adjust" a glaze by using different temperatures, but I feel the results are a bit risky and it's not really something I'd attempt to do on purpose.
I'd rather adjust the glaze chemically to achieve the desired result rather than play with maturing temps.
In other words, I have a gloss black and a satin black(which you'll see later) that both mature at the same temps.
Anyways, time to move on and finish up Teathingy No.2(working title) and get that in the kiln.


Steve A said...

Or, you can conclude that the revised look is actually pretty cool. Which is actually why it's that way.

John Romeo Alpha said...

May Vulcan, the Roman god of fire, be with you, and bring accuracy to your cones, and desired results to your glazes.

limom said...

Steve A, yeah, it's sort of growing on me.
Besides, I'm might be too lazy to fire it again.

JRA, electric firing is pretty routine.
Wait till we get the gas kiln set up, for sure an offering to the fire gods is required.

RANTWICK said...

If I had one of those I might start drinking tea...

limom said...

Soon the whole world will be drinking tea!