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when to underglaze


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#1 mark s

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Posted 02 February 2013 - 10:52 PM

Hi All,

Long time lurker, first time poster. I'm just starting to experiment with underglazes and have a question. I keep seeing articles that talk about applying them to leather hard, bone dry or bisqued clay. Would you ever want to apply them to wet clay or would that cause the pot to colloapse?

Thanks, Mark

#2 Iforgot

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Posted 02 February 2013 - 11:22 PM

How are you thinking of applying the undergaze? Collapsing is a possibility in some cases, but not all.





Darrel
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#3 Benzine

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Posted 03 February 2013 - 12:03 AM

You could apply them to clay that is on the workable side, you would just have to be more careful, especially if you are applying it with a stiffer brush, that could put more pressure on the clay surface. Also, I would imagine, that if the clay was really wet, the underglaze could bleed a bit, and you'd lose some precision. Personally, I don't apply underglaze, until the clay is leatherhard.
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#4 mark s

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Posted 03 February 2013 - 12:15 AM

How are you thinking of applying the undergaze? Collapsing is a possibility in some cases, but not all.





Darrel



Thanks for the response Darrel. When i was a kid there was a toy (can't remember what it was called) where you dripped ink on a spinning piece of paper and it would create these random, almost Rorschach looking patterns. I wanted to try something similar on shallow bowls and platters before i cut the bat. It may take more speed than wet clay can handle. But that's what I hope to find out.

#5 mark s

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Posted 03 February 2013 - 12:26 AM

You could apply them to clay that is on the workable side, you would just have to be more careful, especially if you are applying it with a stiffer brush, that could put more pressure on the clay surface. Also, I would imagine, that if the clay was really wet, the underglaze could bleed a bit, and you'd lose some precision. Personally, I don't apply underglaze, until the clay is leatherhard.



Thanks for the input. A related question. I'm using Amaco's Velvet underglazes. All the literature I read says they can be fired succesfully at cone 6. The info on the jars say cone 05-04. Did I get the wrong underglases or will this work?


Mark

#6 JessicaGrayCeramics

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Posted 03 February 2013 - 05:34 AM


You could apply them to clay that is on the workable side, you would just have to be more careful, especially if you are applying it with a stiffer brush, that could put more pressure on the clay surface. Also, I would imagine, that if the clay was really wet, the underglaze could bleed a bit, and you'd lose some precision. Personally, I don't apply underglaze, until the clay is leatherhard.



Thanks for the input. A related question. I'm using Amaco's Velvet underglazes. All the literature I read says they can be fired succesfully at cone 6. The info on the jars say cone 05-04. Did I get the wrong underglases or will this work?


Mark


Mark,

Even though they say cone 05-04 some of the colors do work well at cone 6. It is a hit and miss thing. Different colors have different results at cone 6. I recommend as with most glazes do a test before using it on your actual work. Sometimes the bottle will tell you they work okay up to cone 6, sometimes it will not. It is best to test it on a sample tile of like texture to your work. I might also add you may want to put a little punched bowl underneath the sample in the kiln in case it would for some crazy reason completely melt and run really bad. This should not be the case, but it is best to be prepared. Good luck.
Jessica Gray, MFA
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#7 Marcia Selsor

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Posted 03 February 2013 - 08:15 AM

There are always exceptions in ceramics. I apply underglaze at bone dry stage. I don't have to go over areas several times because the underglaze is absorbed faster to dry clay. There are recipes for underglazes for leather hard, dry, bisque stages depending on your needs.
Commercial underglazes gives directions. Depending on what you re doing, workability of the surface can require applying at a soft leather hard stage.

Marcia

#8 SShirley

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Posted 03 February 2013 - 10:15 AM

I think that was called "spin art". It was popular at fairs and places like that. Doing it on clay is a cool idea. Let us know if you get it to work.

#9 Denice

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Posted 03 February 2013 - 10:57 AM

Mark you maybe able to get a color chart from Amaco showing the underglaze fired at C04 and C6. Duncan gave me one when I was working on a large fountain project, the colors are a lot brighter and intense at 04. I used the brightest colors on the chart so when I fired them at a higher temp. they would still have some punch. Denice

#10 cracked pot

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Posted 03 February 2013 - 11:32 AM

Hi All,

Long time lurker, first time poster. I'm just starting to experiment with underglazes and have a question. I keep seeing articles that talk about applying them to leather hard, bone dry or bisqued clay. Would you ever want to apply them to wet clay or would that cause the pot to colloapse?

Thanks, Mark



Mark,

I just had week with my four year old granddaughter and we used Amaco Velvet underglazes on cone six white clay. The bowls with the snakes and the turtle were painted bone dry the once fired with clear Amaco glaze. The other two bowls were painted on bisque fired bowls, glazed with clear on the inside and Potter's choice on the outside. All were fired together to cone 6. Colors come out darker that you would think, so we mixed some white with the dark green to make it lighter.
Hope this helps,

Fran

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#11 Chris Campbell

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Posted 03 February 2013 - 11:32 AM

That spin sounds like a great idea ... The one thing I would say is you might want to spin the colors one at a time and maybe quickly blow each color dry before the next layer. Since your clay is wet they won't absorb quickly and you might end up with them dripping together into muddy brown.
Yes, those underglazes fire to Cone 6 ... most just get darker. Amaco shows color chips of both in their catalog and probably online too. I have fired some of them to Cone 10.

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#12 Chantay

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Posted 03 February 2013 - 10:49 PM

I've used underglazes many times. I have used them on both green ware and bisque. On earthenware and stoneware. One thing I discovered using a cone 6 stoneware, the colors stayed more vibrant if applied to the green ware, then bisqued, then a clear glaze for final fire. This is instead of applying to bisque and then putting a clear glaze on top. Did this make sense??

-chantay
- chantay

#13 Bette

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Posted 03 February 2013 - 11:18 PM

Here is the Duncan info about performance of its underglazes at ^6:
http://www.bigcerami...-RangeIndex.pdf

#14 kathi

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Posted 04 February 2013 - 02:32 PM

You could do your "spin art" on bisque. That way you wouldn't have to worry about unintentionally "altering" your pot.
You could also do "spin art" on leather hard pots, but use colored slips!
Good times....

#15 Idaho Potter

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Posted 04 February 2013 - 09:38 PM

I think Kathi has the right idea. If I were applying color to a wet stage pot, I'd use slips, not underglazes.

As to underglaze, I apply them to bone dry and then I bisque the work. This does two things, the underglaze adheres better, and bisquing "sets" the color so it won't smudge or smear. It also allows you to touch up the color after the bisque firing--in case you didn't apply enough coats. I apply three coats of underglaze--either one color solid, or variations of hues to give some depth. Underglazes for the most part can be mixed--just as you would paints--to increase your color palette.

Shirley




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