Working with Clay 5: Glazing (Glost-Firing)

 Choosing the Right Glaze:

Note: It’s important to remember that the colors of the glazes before firing are not necessarily the colors they will look like after firing. Your studio should have a glazing reference chart to consult.

Crazing is when the glaze cools in such a manner that it weakens the structure of the vessel underneath, pulling it apart so that it’s very weak and wants to shatter when cooled. It might look sturdy but it’s not. Crazing happens when you mis-match a particular glaze with the wrong kind of clay. Just as there are low-fire and high-fire clays, there are also low-fire and high-fire glazes.

Painting your Glaze:

You can put down temporary stickers (or cut tape to shape) and glaze over it, then pull the stickers off when it’s dry before firing, to get various shapes.

NOTE: Be very careful not to glaze the bottom of your vessel! If you do, it will glue to the inside of your kiln, and there's no way to remove it without chiseling it off - destroying your vessel in the process.

Firing Glaze Ware

Depending on the kind of clay and glaze you use, you may choose a low-fire or high-fire program. FCPS recommends the following settings:

Low Fire Glaze

Stage        Ramp            Temp        Hold

1                9999 (full)    1200°F    10 minutes

2                9999 (full)    1850°F    10 minutes

High Fire Glaze

Stage        Ramp            Temp        Hold

1                 9999 (full)    1200°F    10 minutes

2                 9999 (full)    2150°F    10 minutes

These settings are faster than bisque firing, often taking about 3 hours to get up to the highest temperature.

 

Underglazing

 

Ceramic Pencil

 

Crackle glaze

 

To get a crackle, use not too much, not too little.

 

Leopard Skin Glaze

 

Oxides

 

Resist Slip & Glaze for Raku

 

First you burnish the vessel and bisque fire it. Then you use the resist slip and a “clever glaze”. First you apply the resist slip a temporary barrier protecting the burnished surface. Then, you add a paper stencil. Whatever is exposed will be black.

 

Raw Glazing

 

When you glaze on leatherhard clay. It can’t be wiped off if you don’t like it.