Slip vs. glaze?

[mdc]

Hi everyone! I teach university-level anthropology/archaeology courses and I have two question that have been stumping me for some time: How can you tell if a pot has had a slip applied to it, and how can you tell the difference between a slip and a glaze? I know the difference in material and application method, but I can't figure out how to tell the difference! Any info would be helpful to me and my students! thank you!

[Natas Setiabudhi]

As general slip has a dominant clay in a mixture such as ball clay and china clay, meanwhile the flux (whiting, feldspar) and the glass former (quartz) as auxiliary substance. In some ceramics book slip sometime called engobe. While the glazes are vice verca, the flux and the glass former are predominant. I hope this comment don't make you satisfied, so we can discuss deeper...

[Chris Campbell]

Great question that really got me thinking ... I look at a pot and can usually tell but how?

Well, sometimes it's obvious as the slip is raised off the surface ... or the glaze is fluxed and shiny ... those are the easy ones. Another clue is that not many potters use glazes for any surface decoration that needs to be well defined and stay within its boundaries ... well, except for majolica which stays put during firing. Most glazes move on the surface of the pot during firing, so are not suited to painterly decorations unless multiple steps are taken. So if the decoration is sharp and detailed it is probably slip or underglaze ... but as I'm sure you have already noticed, not always.

[Marcia Selsor]

And then there is Terra Sig...to throw a whole 'nother spin on things.

If you look at Pueblo pottery black on black...the shiny parts are burnished. The dull surface has been made dull by reintroducing water or slip back over the burnished surface. Still there is no glaze.

 

Marcia