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Underglazes should be applied when?


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Just read this on another website... Is this true?

 

"When to Apply- Underglazes should be applied to dry greenware. If greenware is still damp when applied, the underglaze colours may chip off after firing."

 

I've read here and elsewhere that underglazes can be applied to leather hard clay all the way up to dry greenware. Some even say they can be applied to wet clay if you can do so without brush strokes ruining surface. So which is true? If I paint on leather hard clay and then allow the underglaze and clay to basically dry together until bone dry and ready to bisque fire will my colors chip off?

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I usually paint on the underglazes at the leather hard stage which I find the best time. I have also put them on before this and when bone dry. I have never had underglaze chip off. I then add more colour if necessary after the bisque firing.

 

 

 

 

 

 

 

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post-12043-136274461695_thumb.jpg

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This is an interesting question as ceramics is still changing.... I attended a Mayco Knowledge Workshop last summer where we used underglaze (true underglaze, not their Stroke & Coat) on cone 04 low-fired bisque and then immediately applied their clear glaze on top without firing first. We then fired once to cone 06. The piece came out beautiful with no crazing, shimmering, pealing, cracking, etc. Mayco has reformulated their underglazes to allow it to be applied to bisque and clear glazed over before firing. It's truly amazing in my opinion. Mayco is doing a top notch job at innovating! Keep in mind, this only applies to Mayco underglaze that I know of...

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If underglazes are applied to leather hard or wet pots, they should actually bond even better, not flake off.

 

Any good brand of underglazes can be applied to wet, leather hard, bone dry or bisque ware. If you apply them to bisque you do not need to fire them before glazing, but you should let them dry overnight if you're dipping the clear glaze.

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Just read this on another website... Is this true?

 

"When to Apply- Underglazes should be applied to dry greenware. If greenware is still damp when applied, the underglaze colours may chip off after firing."

 

I've read here and elsewhere that underglazes can be applied to leather hard clay all the way up to dry greenware. Some even say they can be applied to wet clay if you can do so without brush strokes ruining surface. So which is true? If I paint on leather hard clay and then allow the underglaze and clay to basically dry together until bone dry and ready to bisque fire will my colors chip off?

 

 

I use the AMACO velvet underglazes and have applied them at all stages from wet to bone dry and on bisque ware. I have not had any trouble with them flaking off but I suppose if you really glop it on they might. You may want to make a few test tiles with the underglazes you use just to be sure how they will react.

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LOL okay I guess that little tidbit falls under the Catagory of not believing everything you read.

 

I am using Amaco LUG underglazes but have only just started using them and have not even seen them fired to bisque yet. When I read that I was just worried that the few pieces I have painted and left drying in class had been done incorrectly and were going to flake off since I painted the underglaze on at the leather hard stage.

 

Thanks for all of you that let me know the accepted ways in which to apply underglaze to clay.

 

Terry

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LOL okay I guess that little tidbit falls under the Catagory of not believing everything you read.

 

I am using Amaco LUG underglazes but have only just started using them and have not even seen them fired to bisque yet. When I read that I was just worried that the few pieces I have painted and left drying in class had been done incorrectly and were going to flake off since I painted the underglaze on at the leather hard stage.

 

Thanks for all of you that let me know the accepted ways in which to apply underglaze to clay.

 

Terry

 

 

I've tried a few of the AMACO LUG underglazes as well and I didn't have any problem with flaking no matter when I applied them.

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I use the AMACO velvet underglazes and have never had a problem with them flaking off the piece. I've used them on all stages of raw clay and on bisqued pieces (depends on the end result I want to achieve). As a note, the youth coordinator at the school where I use to work would let the children paint underglazes on their 'just created' pieces, then after they dried, she would apply a clear glaze and fire. They turned out great.

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I mix Glomax with my porcelain decorating slip, i.e. slip made from my clay body. By adding Glomax, Calcined Kaolin, it doesn't shrink as much and does not flake.

I am after an opaque color and the bone dry surface sucks in the slip to achieve this affect. So as I said, it all depends on what you are trying to do.

 

 

Marcia

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  • 6 years later...

Yes, essentially.   Get yourself a good basic studio guide, like Vince Pitelkja's Clay: A Studio Handbook, or similar.  A Google search will yield good basic info as well. (I am assuming you already searched the forums and thus found this old thread).  Books are still more portable than electronics, so I find having a print material is useful.  You'll want to know soemthign about the brand/type of underglazes you'll be working with, to be sure they're likely to be right for the clay body & the clear glaze being used. Transporting greenware is always dicey---maybe work on bisque for conveniencesafe travel--obviously a personal decision-underglaze prefers greenware, in my opinion, but that's not written in stone. Welcome tot he forums.

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what you plan to do is good.   the transportation of any greenware can be made safer by thinking hard about where the piece will be safest in the vehicle.  i use a lot of upholstery foam as a base for everything.  (old sofa pillows are great, new foam is very expensive.)  your angels sound delicate, support them with some kind of soft towelling or fabric so the wings will not be stressed.

one cheap item is the swimming noodles that are sold at the dollar tree stores.  you can cut them easily.  they are not really soft, but they can provide a frame to keep pieces from sliding into each other.   an old bath towel laid over the frame gives a "pocket" of softness for the clay.   think egg carton.

the sudden shock of an emergency stop might ruin everything anyway but providing a soft nest for each piece will help you get them safely from studio to home and back again.

 

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  • 1 year later...

@Purpleglaaze, if you are using a brushing glaze you can lightly sponge on a thinned down coat of glaze, let that dry thoroughly then brush on the remaining coats. Other thing about glazing over unfired underglaze (ug) is the ug contains gums that can hinder the amount of glaze taken up by the bisque. When you bisque fire ugs the gums burn out so the bisque takes on the glaze easier. There are ugs that can flux enough at bisque 04 that also can hinder the glaze application. Like its always said, test, test, test.

Welcome to the forum!

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@Purpleglaaze I have spent a good bit of time covering underglazes and as above they usually affect the porosity for all the reasons mentioned  as well as they just plain old fill in the pours of the body. Whenever spraying these, even after bisque the areas of heavy underglaze  often require a thin even coat and extra drying time compared to the rest of the claybody. Fortunately with some patience and smooth light coats it’s pretty easy to get a uniform glaze thickness. If the glaze allows, I will use a heat gun set on low  to dry those areas in between coats. All inside a paint spray booth with proper PPE of course.

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  • 4 months later...

Hi!

My question is a little bit different. I underglazed a greenware piece. The color looked fine after bisque firing but got really faded after cone 5 firing. So I was wondering, since there is no glaze on top of the underglaze, if it was possible to re-underglaze the fired piece and then refire it.

Thanks for letting me know!

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52 minutes ago, baby-egg said:

if it was possible to re-underglaze the fired piece and then refire it.

I think it’s possible but getting it to stay with proper thickness  may be difficult and if fired to cone 5 will stress the pot a bit and .... likely make the color fade away a bit as well. Testing is the only way to know how well this underglaze will perform. Another possible fix would be to use lowfire products like stroke and coat and fire down to 04. Even China paints provide some opportunity but they usually melt into a glazed surface..

below is a mug where lowfire products were applied as decorations a cone 6 pot  in steps and downfired. It may give you an idea of something to try.

8737150A-F2A9-451F-AC48-E23D1E343FFE.jpeg

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  • 3 weeks later...

Thanks all for the helpful tips here. A few years ago, I started reviving an interest in clay sculpting helped by my sons' middle school art teacher. Using Amaco velvet underglazes and glazes, I'm now experimenting with applying them on greenware and had mixed results. A couple of pieces had quite a lot of flaking (e.g., a black cup with red dragon), but they were sitting with underglaze for about 3 years before firing; so, as mentioned here, the dry clay may have been the problem.  Others done since March break (e.g., the black/red dragon & stump) came out well except for a few pinholes. I haven't tried applying the colors to leather hard clay yet, so will do that next.

What are good ways to avoid or minimize pinholing or flaking when painting greenware? I usually apply 2 coats each of underglaze and clear glaze. Would it be better to use just 1 coat of each or apply it very thinly? The safest method seems to be to use just underglazes, then apply glaze after touching up for a second firing; but this doesn't allow nice blending of colors. 

Though I've been advised to bisque fire before applying any colors, I prefer working with greenware and underglazes because it's more efficient and resulting colors seem beautifully consistent. With pieces that were baked first before a colored glaze, the result was a mottled color (lighter at high points, darker at grooves and lower edges). But with even a green glaze on greenware (e.g., the stump) the color still came out very even, with no running. Cheers.

2021-04-21 15771b.jpg

2021-04-21 15769b.jpg

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Also, can areas with flaking or pinholing be fixed somewhat by adding underglaze and glaze again for a 2nd firing, or will new colors on a glaze flake off and the 2nd firing damage the colors that came out well the first time?  I'm about to try this.  All the clay and glazes are for low firing. 

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