Underglaze versus glaze?

[Gregory Hendren]

I read the Paul Wandless article in March/April Pottery Making Illustrated about mixing underglazes.  I'm creating abstract sculptures out of clay.   

I realize that underglazes can be mixed to create new palettes that aren't available straight out of the jar.  What are the advantages of mixing my own colors and then covering with a clear glaze such as semi-gloss or gloss when there are fifty or more commercial glazes ranging from transparent to opaque? 

One brand, I don't remember, offers glazes that start from transparent to opaque depending upon the number of coats, ranging from one, two or three.

Also, when would you use glazes over underglazes if at all? 

All help will be appreciated.  I've bought dozens of glazes and dozens of underglazes and the process is becoming overwhelming.

Many thanks.

Greg

 

[Min]

Underglazes can be left unglazed to create a matt look similar to engobes or coloured slip but the surface won’t be as smooth as a  glazed surface. I’ve had just a few Spectrum underglazes flux to the point of becoming glossy at cone 04 but mostly they stay matte at that cone. Using a clear glaze makes the colour pop.

Underglazes allow you to blend and layer colours in a way that would be very difficult to do with glazes. Some lovely examples by Terri Kern here.

edit: for functional pots underglazes should have a food safe covering glaze 

[AndreaB]

48 minutes ago, Min said:

Underglazes can be left unglazed to create a matt look similar to engobes or coloured slip but the surface won’t be as smooth as a  glazed surface. I’ve had just a few Spectrum underglazes flux to the point of becoming glossy at cone 04 but mostly they stay matte at that cone. Using a clear glaze makes the colour pop.

Underglazes allow you to blend and layer colours in a way that would be very difficult to do with glazes. Some lovely examples by Terri Kern here.

Hi Min, I've done the underglaze blend fire to maturity but found that on one piece a scratch developed which wasn't there after firing. Apart from glazing with a matt how do I go about protecting the surface?

[Benzine]

I just tell my students, that underglazes are essentially like a paint, that can withstand thousands of degrees.  They mix like paint, apply like paint, can be layered like paint and GENERALLY, what you see is what you get.  I do have a couple underglazes that do change color pretty dramatically, like Amaco's Dark Blue.  It looks like lavender before it is fired. 

But I recommend the underglazes if the student wants to do some detailed/ precise decorating.  A poster her, Guinea Potter did some AMAZING illustrative decorating, with underglazes.

With glazes, I tell the students it's almost the exact opposite.  The colors run, bleed, mix with lower layers, and usually dramatically change color. 

The first project we do is a pinch bowl, where I require them to use both underglaze and glaze, along with a variety of techniques like sgraffito, underglaze with an oxide stain, resists, etc.

[Gregory Hendren]

Hi Min,

Thank you for taking the time to clarify this issue and to include a site to view.  (I may ask a follow-up question!)

Cheers,

Gregory 

[Gregory Hendren]

Hi Benzine,

I am trying to achieve some solid colors on some shapes and then several layers on others.  For instance a layer of blue, light blue, green.

Would you recommend using an underglaze  base coat for the multi-layerd application, or am I wasting the ug since it will likely be covered?

Thanks.

Gregory

[Min]

23 hours ago, AndreaB said:

Hi Min, I've done the underglaze blend fire to maturity but found that on one piece a scratch developed which wasn't there after firing. Apart from glazing with a matt how do I go about protecting the surface?

Duncan sells  clear sealers, both matte and gloss, that would help protect it. Some underglazes flux more than others and create a better bond with the clay than others. (If you do try the spray I would try it on a test piece first) If you can't get Duncan or a similar product where you live I would try a non yellowing acrylic spray from a hardware store.

[Chilly]

What @Benzine said 

[Benzine]

On 5/16/2018 at 8:41 PM, Gregory Hendren said:

Hi Benzine,

I am trying to achieve some solid colors on some shapes and then several layers on others.  For instance a layer of blue, light blue, green.

Would you recommend using an underglaze  base coat for the multi-layerd application, or am I wasting the ug since it will likely be covered?

Thanks.

Gregory

Underglazes would work well for that, as long as you aren't expecting them to mix during firing. 

So you want a solid background, with some shapes of other colors on top, is that right?  If so, underglazes will work great for that.

[Gregory Hendren]

Thanks Benzine.  I appreciate your advice.