Glaze, Oxides and Stains

[bont]

Hello,

I've been wondering for a while now about the differences between glaze, oxides and stains. I've googled the question many times but never got an answer. I'm watching a show, The Great Pottery Throwdown, and when the bisque stuff are ready to fire, the MC would say "Over here, we've got the oxides and the glazes". So yeah, how are they different? Thanks.

[Chilly]

My opinion, others will have their own opinion:

• Glaze - makes a finished surface, may include colour or be clear, usually glossy,  most dinnerware is glazed
• Stain - used to colour glaze or underglaze
• Underglaze - purely colour, doesn't usually give a finished surface, not usually glossy
• Oxide  - metalic substance, also used to colour glaze and underglaze, can  be used like an underglaze or on it's own.

 

They're all words that are used interchangeably by both knowledgeable potters and TV presenters.  Remember that "throwdown" is entertainment not educational.

 

 

[oldlady]

chilly, it seems that there is a difference in terminology across that ocean, not only in the UK but on the continent as well.  wondering how the difference can be explained so we all can understand.  the polish pottery factories use color applied with sponges cut in various shapes.  their translation of what is being used is not quite clear to me.  seth cardew demonstrated his use of color at a workshop here and when he ran out of blue, he asked for some cobalt (not specifically carbonate or oxide) and mixed it with water to make his beautiful birds.  just a wash, to my way of thinking.

hope someone can clarify it all,  thanks for the question, bont.

[liambesaw]

Glaze: a glassy matrix generally composed of clay, Feldspar, silica, flux and colorants

Oxides:  specifically natural mineral colorants, carbonates are also rolled into this category.  Iron, cobalt, copper, manganese, chrome, tin, titanium, zirconium and others will impart a very strong coloration to clay, slip and glaze.

Stains: stains are standardized "fritted" mixtures of oxides which are reliably and consistently the same.  These are an important element to commercial pottery as the colors do not shift.  With oxide colorants, since they're mined minerals, they can vary in color drastically from batch to batch.  Fritted means they're fired into a glassy matrix and then reground into a fine dust.  With stains generally WYSIWYG, whereas an oxide can appear black but fire to blue. Or appear brown and fire to yellow.

 

Hope that helps.  Oxides (in this case) and stains are often just colorants that are used in formulating glazes, but are sometimes used as a strong colorant on the clay body, or over or under glazes.