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Judith B

Underglazes Vs Glazes

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So, this is a very trivial question but I can't find a proper answer anywhere.

What is the difference between an underglaze and a glaze? From what I read online, it seems that it is pretty similar, only a small variation of some chemicals. But which ones?

I understand that slips are made of clay and stains but I can't quite figure it out for underglazes and glazes.

Where I work, we have underglazes and glazes and sometimes people ask the difference... And I always feel very stupid ^^. I know that we have to glaze the underglazes but it technically doesn't make much sense to me

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Underglazes are for decorating ... They do not seal the surface or make it food safe. They will not prevent stains or color absorption. They are most often used under glazes.

 

Glazes when properly matched to the clay and properly fired, seal the surface with a glass like layer making the wares suitable for utilitarian use.

 

A glaze that does not move much during firing can be used for decorating but an underglaze cannot be used as a glaze.

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Underglazes are the color. They are similar to oxides, except oxides are reactive to the chemistry around them, either in the clay or the glaze or both. Underglazes are made non reactive. They are also usually the color they will be albeit not the same intensity. They can be left unglazed, but I think they are just decorative at that point. They probably would be in danger of abrasion or wear.

A glaze is almost a glass that is melted on to the ceramic in either it's green ware state or its bisque state.glass has to be compatible in what shrinkage and expansion each glass has .if too far apart , they come apart. Clay and glaze have those same issues, plus other issues to do with the clay body. So glazes don't always work even if They are fired to the same cone . Some clays have fluxes, or chemicals that become fluxes in them and they become self glazing. Wood fired kilns can glaze the vessels in the kiln through a deposit of wood ash on the vessels. Adding salt to kiln (not electric unless made for it, ruins the elements) glazes it too. Since clays and glazes have a lot of the same things in them, clays can almost become glazes if chemicals are introduced .

The purpose of bisqueing is so that the ceramic is still able to accept the colorant and the glaze but not be as fragile as greenware. Once the vessel has been fired to the point of maturity ( so it is completely fused on a molecular level) It is all but impossible to put glaze on (. I don't know about oxides or underglaze- perhaps they might take if there was tooth). Glaze would slide off I think.

Dealing with clay is chemistry or alchemy or both. I think I might learn a few chants to get thing more on my side. Nah it would probably backfire! Jolie

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Underglazes are good for detail work. I paint my detail work on greenware than fire to bisque 04. That way when I put my glaze on, it won't pull the underglaze off. 

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Try putting two glazes side-by-side to produce detailed pictures then repeat with under-glazes.  Fire both and see the difference.  Under-glazes do not move or blend with each other.  Most glazes (I know not all) will bleed into each other, or one will move over the other, or they will slide slightly down a vertical surface.  

 

For me, under-glazes are for when you want more than one colour on a piece, glazes are for single-colour or "doesn't matter" if they run together.

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The descriptions above are more accurate, but to keep things simple, someone said to me an underglaze is like colored slip and a glaze is more of a glass coating.

 

It's prety much the way I think of it to this day

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So, are there recipes to make your own underglazes?  I have lots of books for making glazes but they don't have recipes for underglazes.  I have lots of Mason stains and clear glaze so this sounds like a fun thing to do if I knew how.

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So, are there recipes to make your own underglazes?  I have lots of books for making glazes but they don't have recipes for underglazes.  I have lots of Mason stains and clear glaze so this sounds like a fun thing to do if I knew how.

Check the handouts on engobes and underglazes and on Mason stains at Vince Pitelka's website: http://iweb.tntech.edu/wpitelka/syllabi-handouts/handouts-info.htm

 

You may also find recipes in the various Robin Hopper books and other sources.

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So, are there recipes to make your own underglazes?  I have lots of books for making glazes but they don't have recipes for underglazes.  I have lots of Mason stains and clear glaze so this sounds like a fun thing to do if I knew how.

Check the handouts on engobes and underglazes and on Mason stains at Vince Pitelka's website: http://iweb.tntech.edu/wpitelka/syllabi-handouts/handouts-info.htm

 

You may also find recipes in the various Robin Hopper books and other sources.

 

Thank you.  I'm just starting back up in pottery after a few years off after a broken wrist and a move to Texas.  I had been going to a local studio where we fired to cone 10 reduction.  I now have my own kiln and will be firing to cone 6 oxidation.  The problem is I have left over cone 10 clay that I want to fire before starting on cone 6 but I don't want to invest heavily in cone 10 glazes.  I have a clear glaze that will fire from cone 5-10 so would like to do some slip work and now the idea of the underglaze is intriguing.  Lots to learn - which makes it fun.

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So, are there recipes to make your own underglazes?  I have lots of books for making glazes but they don't have recipes for underglazes.  I have lots of Mason stains and clear glaze so this sounds like a fun thing to do if I knew how.

 

I think commercial underglazes are well worth the money. If you get the right brand (I use Speedball), the colors are stable at cone 6, they brush on very nicely, and can be applied at any stage- wet, leather hard, bone dry, or bisque. Personally, I like to apply to bisque since they dry quickly that way, and I the work isn't as fragile at that stage.

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The descriptions above are more accurate, but to keep things simple, someone said to me an underglaze is like colored slip and a glaze is more of a glass coating.

 

It's prety much the way I think of it to this day

So, Underglazes do contain some clay? I wasn't sure.

I know how to use udnerglazes and glazes but I was wondering about the difference in composition. Thank you for all your answers :)

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Commercial underglazes fuse more than a slip would. That's why they can be used on bone dry clay and bisque ware without flaking off. They can be fired in bisque and still be porous enough to take glaze. But they don't go into melt like a glaze. They are quite versatile. Most home made underglazes are either more of a colored slip that has to be applied to leather hard pots, or are just stains with a frit binder and work best on bisque. I was working on a new commercial underglaze formula when I left my last tech job, and I can tell you that they are fairly complex. It's a fine balance to get them to fuse to leather hard, bone dry or bisque, but still be porous enough to take glaze after bisque firing, to play nicely with glazes, and to brush well.

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