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About Firing Glazes: Article or Project


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The first thing I want you to do is pay attention to the labels and instructions that come on the jars of glaze. READ THEM

The labels will tell you the recommended firing temperature/cone range. It will tell you if the glazes are compatible with each other. It will tell you if the greenware needs to be fired hotter (and how much hotter) than the glaze.

Some glazes cannot be fired in the same kiln load. Most of the more modern glazes are compatible, but some are not. At one time you could not fire red and green glazes in the same load or the colors would jump. So it is better to be safe than sorry. KNOW YOUR PRODUCT.

Most glazes have a firing range. Some fire at 04-05, some at 04-06, some at 05-06. All of these can be fired in the same kiln load. To do this, you find the lowest common cone. From the examples given, all can be fired at cone 05.

Typically, glazes should be fired between one and two cones cooler than the bisque (fired greenware). Some special effects require they be fired at the same temperatures as the greenware.

It is not a good idea to fire glazes and greenware in the same load, though it can be done. It will only take one disaster to stop you from doing it again.

You can fire glaze ON greenware as long as it does not cover more than about 10 percent of the total surface. For example: areas where you plan on applying fired gold to accent a piece that you are planning on staining. Please do not glaze the interior of items in greenware, this can only result in crazing. You may not see it right away, but over time, your glaze surface will develop hairline cracks.

Once you know what temperature an item needs to be fired at, the rest is simple. Just follow the same basic steps to load and fire your kiln.

With glazes, you will need to use stilts under your pieces. Stilts are ceramic bases that have teeth or prongs on them that are used to support glazed items during the firing process so that they will not fuse to the shelving. The ceramic base goes on the shelf with the pins up. The glazed item sits on top of the pins.

It is more important with glazes than with greenware, that the kiln is not open until fully cooled. Premature opening can cause great stress on the ware and can create crazes/cracks in the glazes and can even cause the item to break from thermal shock.

WARNING: Stilt marks can leave glaze shards that are VERY sharp. Handle carefully and sand them off with a stilt stone or small drill bit to prevent future cuts or scratches.


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