Saturday AM Pottery

Stains, washes, underglazes and overglazes

Stains, washes, underglazes and overglazes are very much the same.  Stains and washes are essentially different terms for the same thing.  They can be used under a glaze or over it and thus become “underglaze” or “overglaze”.  And engobe is a stain which has clay added to it to help keep it from shrinking.  Slip and engobe are pretty much the same except that engobe refers to the addition of color to the slip.

Using a stain as an underglaze creates more defined patterns and colors.  As an overglaze, they “bleed” out more.  If you want to do an intricate design, you’d use underglaze directly on the bisque ware.  A design done as an overglaze would be more diffuse.  So, a simple design would be more effective as an overglaze.

Use iron oxide and cobalt added to manganese to make a good black.  Cobalt and manganese are quite toxic.  Avoid prolonged contact with skin.  Wear gloves to work with them, especially if you have any cuts or scrapes on your hands.  Wearing gloves is always a good idea when working with glazes and stains as all materials may be toxic over time.

Underglaze base can be purchased or mixed up.  Use a ratio of 2:1 of ball clay and silica to make a good underglaze base.  Then add oxides or stains (essentially the same thing) and water to a cream like consistency.

Stain = metallic oxide + water

Underglaze = metallic oxide + underglaze base + water

Underglaze results in more intense color than just a stain.

Add extra silica to an underglaze to help it stick to the bisqueware, but not too much or it will run in the glaze kiln.

It is also possible to use metallic oxides to color slip or clay.

Generally, a lot of red iron oxide is needed to get a strong color.

Let layers dry before adding another layer.