Firing Questions.

[Abstraction]

Hello all! I need some clarification on kiln firings & a little help identifying some glaze problems.

So first, I've been taking classes at a community center. I have ceramics/pottery background but I don't know it all when it comes to firing a kiln. I know the basics and I've loaded/fired bisuqe kilns and low/mid fire glaze kilns [it's been a couple of years though]. My issue/question here is:

 

I've noticed that some greenware has been loaded into a low fire glaze kiln [cone 05 I believe].

Is this okay to do? I have never seen it done before & just wanted to make sure it wouldn't jepodize the integrity of the work.

 

Also, there has been issues with glaze crawling and peeling all over peoples work. Does this sound like a dust issue? I've never had issues with dust before so this is a new concept to me.

I'll have to post a picture later.

 

Thanks!

[Benzine]

Welcome to the forums.

 

First off, there is nothing wrong with firing greenware, of any clay body, with a low fire load. Most people bisque to 04 or 05, so it does save time, and resources.

 

The draw backs: The off gasing, from the greenware, can effect glazes nearby. Secondly, and this is why I avoid firing greenware and glazeware together in my classroom, thick wares, and others that are seemingly dry, can explode, and then stick to the glaze of the glaze ware. It seems that the only time, that I do have greenware explode, is if I try and fire it with glazeware.

Generally, it isn't a problem.

 

As for the crawling glaze, I would say dust, or more likely skin oil, is the cause. I rinse my wares, before glazing, and have my students do the same. I wash my hands frequently when glazing, and never put lotion on, when I'm going to glaze.

[High Bridge Pottery]

Recently I made some quite thin bowls. Thinner than my usual style. I found where they were thinnest I got crawling. I put it down to soluble salts coming to the surface where it dried too quickly in places.

 

Could be that or as above post.

[neilestrick]

If you want to bisque and glaze fire in the same load, put the glaze work at the top of the kiln, greenware at the bottom. That way if the green pots blow up they are less likely to get onto the glaze work.

 

Crawling can come from dust, oils, glazes that don't like to play nice together, glazes that are too thick, or layers of glazes that are applied while the previous layer is too wet (especially easy to do on thin pots).

 

What you describe as peeling- do you mean the glaze is flaking off after firing?

[Cavy Fire Studios]

Flaking glaze--you mean shivering? Most of the time, that happened because either my slip was slogged on too thick, or the clay/casting slip contained lithium in its recipe. Lithium clays are notorious for making glaze shiver off! Check with your supplier if this seems to be a common issue.

[Benzine]

Shivering would be the glaze getting compressed.  With crawling, the glaze moves away from the spot.  If the glaze is coming off the wares, then yes it would be shivering.  It sounds like the glaze is just moving away and leaving bare spots.