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Underglaze Issue

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The thumping noise you hear is my head against my wedging table.

 

So first I switched underglazes from closed down local co. to Amaco.  Then I switched to a new clear cover glaze. Most recent is Laguna Morraccan Sand MSD-29.  I had called Laguna and asked specifically for a clear glaze to cover under glaze.  This is the glaze that was recommended.  I first did a test tile.  Colors looked good.  Well, the tiles were all flat.  When I did some mishima on a bowl with the underglaze it ran.  I have used this underglaze on several other items. Flat items are OK.  Vertical runs.  I will do a round of test tiles next glaze firing but hoping for some suggestions.  Crappy cell phone pic attached for your enjoyment. 

 

 

Well, verizon is holding my pic hostage.  I will post it when there is free space on the inter web. 

 

 

 

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How many coats are you using?

 

I've never had an issue with a clear glaze running.

 

The worst, I've had happen, is the clear will get a little translucent-yellow in spots, if I put too much clear on. 

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I had weird stuff happen with clear glaze over my underglaze when I first started using it. One of the things that happened was the colors, black especially ran like bad ink making everything look blurry, on any vertical surface, I also had some color shifts happening. I switched to Amacos Zinc Free Clear and have had no additional issues. Maybe get a small container and do a test? OH and I also do my underglaze painting on bone dry greenware not bisque.

 

I hope this helps!

 

Terry

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The problem is the glaze, not the underglaze.

I get this question a lot in workshops because people have mason stains change color or colors run after a higher temp firing. So ... I made a large colored, patterned test piece, marked it in sections and used several different glazes to illustrate how they behave. Some sections are different colors, some sections have bled or run and others are fine.

For Amaco under glazes I would recommend using their matching clear glaze ... The zinc free formula works very well for me. It doesn't run and the colors stay true. They make it for cone 05 and for 6.

Pres likes this

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Thanks guys.  I'm just really frustrated lately.  Every time I change one little thing it's like a domino effect and I have three new problems.  I'm going to call Laguna again.  I get all my premade glazes from them.  I have started mixing my own but have not done enough testing to mix any bit batches.  In the process of taking over half the garage for glazing the little studio is just getting too tight. 

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Bugaboo and Chris nailed it.  Amaco underglazes are beautiful and stable. However, most of the time it is a matter of getting the right transparent over top of them as with any underglaze. We used to use the HF-9 for over their underglazes when we were interested in that effect. Originally this glaze was listed as an Amaco High Fire, but now is listed as a Sahara glaze.

I have also used their underglazes under and over a variety of other colors with good effect.

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Thanks guys.  I'm just really frustrated lately.  Every time I change one little thing it's like a domino effect and I have three new problems.  I'm going to call Laguna again.  I get all my premade glazes from them.  I have started mixing my own but have not done enough testing to mix any bit batches.  In the process of taking over half the garage for glazing the little studio is just getting too tight.

 

This cascading effect of making " one little change" has made most of us crazy at one time or other. Go with it and you will learn so much from the experience. I actually think we do this to ourselves when we get bored. : - )

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If I use my underglaze on leather-hard clay, and carve out....and fire.... will it be ok to use clear on? Without fear of running? It should be set after it's been bisque fired, correct? I've learned a lot by reading this thread! :)

 

How is the outcome (look) different on leather-hard vs. bisque?

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How is the outcome (look) different on leather-hard vs. bisque?

I have had mixed results doing this. Sometimes I could not tell the difference and other times the texture or color were very different. The best thing to do is try both on test pieces... Then you know for sure.

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The downside of using underglazes on dry clay is that if you brush on too much or too vigorously you might lose some subtle textures you might want. Also, if you make a mistake you cannot wash it off easily as it sinks in below the surface. The look is different too, as Bob says, but you have to see for yourself if you like it or not.

I have to admit that I probably would not be able to see much difference in a piece that was underglazed before firing or after. I do it for convenience in layering colors without them affecting each other ... e.g. yellow over blue without it going green.

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Neil said what I was going to say, but I'll elaborate a little bit.

 

Whatever colorant is in your underglaze (in the case of the blue, almost certainly some form of Cobalt) doesn't just stay on the surface of the clay when it's covered with a glaze and fired.

 

Cobalt especially is a very strong colorant, very volatile, and will be seeping off of the underglaze'd surface and into the liquid medium of the glaze when it is fired. So once it reaches melting temperatures, the cobalt that volatized into the glaze flows with the rest of the glaze.

 

This will happen whether you apply the underglaze at leather-hard or bisque. The colorant will still seep into the glaze and it will still run.

 

Your best option is going to be a glaze that doesn't flow so much, like the Zinc free one discussed above.

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I've never run into the issue of the clear, making the underglaze flow, but I use Amaco underglaze with Amaco clear.

 

Is the clear acting as a flux of sorts, for the underglaze colorants?

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Benzine, I'm guessing that is what the problem is.  It is kinda funny.  I started with a different underglaze and clear glaze.  But that clear glaze was crazing with my clay.  So I changed clear glaze.  Now I have had to purchase more underglaze but original source wasn't available so I went with the Amaco.  The colors are very vibrant.  But now I have the running.  I have used the underglaze on green ware and bisque and the colors seems the same on both.  I prefer working on green ware.  If it gets messed up I just chunk it and start over.  The underglaze seems to flow across the the moist clay better, sorta like painting, which I have done a great deal of in the past.

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Actually I had an issue of painting Amaco black underglaze on greenware then bisque firing the piece covering with a clear glaze firing and getting running black lines. Something in the black underglaze reacted badly with the glaze somehow. I switched to Amaco Zinc Free Clear and no more issues with running.

 

I prefer painting underglaze on greenware all the way from soft to bone dry. I've noticed the brush strokes seem less apparent when painting on before bisque firing. I have also noticed that some of the blues remain more vibrant if painted on before bisque firing. The red stays brighter if covered by a clear glaze during the glaze firing as compared to firing it to cone 6 with no clear glaze over it.

 

I have found the touchiest underglaze is Dark Blue, which I think includes cobalt as the colorant. It will jump from one piece to another through the clear glaze, it hates the nichrome wire on my bead racks and turns dull and dark after firing when a bead with it painted on it touches the wire. Its such a pretty color that I keep trying it on different things and am learning what it will do and not do.

 

I use underglaze as a painter would and paint scenes, portraits, and such with them on my pieces. I've been training myself to see the colors I want them to turn out like rather than the actual color out of the bottle. I am currently working on more doing shading and washes to improve my gradations between colors.

 

Terry

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Terry, I've never had an issue with my Amaco Black, but I too am not a fan of the Dark Blue. However my issue is with the appearance. It's waaaaaaay too dark. My students want a dark blue, but find it far too dark.

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I've never run into the issue of the clear, making the underglaze flow, but I use Amaco underglaze with Amaco clear.

 

Is the clear acting as a flux of sorts, for the underglaze colorants?

Mason stains and underglazes have some frit/flux in them to help them adhere to the wares when fired. So, you might get bleeding if the flux in the glaze and the frit/flux combine to make it a bit more viscous when melted.

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Benzine - I found that when I painted the dark blue on bisque it came out almost black looking, very un pretty. But I have been playing around and have found that if I paint 1 coat and no more on greenware then bisque it the blue comes out of the glaze fire lighter and brighter and very pretty. I also put down a base coat of white underglaze then the dark blue over it and it really makes it pop. I have decided that I might just know enough to use it on a large set of tumblers and a carrier. This will be the largest item I have tried it on as I have up until now been trying it out on smaller items and boxes. This will be a big test so keep your fingers crossed!

 

I only had an issue with the black until I switched to Amacos Zinc Free clear. When I first started I used the clear the group studio made up themselves. I think it was just a incompatibility issue between their clear and the underglaze. Nobody before me had ever really used underglazes so they never had a problem that they knew of. In fact I had no issue as long as I only used it on horizontal surfaces but anything vertical ran something awful. I went ahead and bought my own gallon of the zinc free clear and use the exclusively over my underglaze work and since then no issues vertical or horizontal.

 

Terry

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Honestly, I'd probably stop getting the Dark Blue, but it comes as part of a reduced price set that I get from the supplier. It has a good assortment of colors, for a good price. So I put up with the one that is just OK.

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I spoke to a glaze tech person at Laguna today.  He recommended thinning the clear.  He couldn't comment on whether the clear glaze I was using had zinc in it or not,  but did direct me to another clear that is zinc free.  Hhmm, yea, and I just did two kiln loads testing this glaze with all my other glazes.  Uuuugh, more bangging of the head on the table.

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Treat underglazes like you would artist's paints.  Mix them.  If a yellow is too brash, add a little white.  If a blue is too dark, add a lighter blue--not white--and you'll find you still have a dark blue, but it won't look black.  There's a great vibrant blue (Marine Blue) that should work great to brighten rather than lighten the dark blue.

 

 I mix orange with yellow to achieve the interior of an orange, or mix with red to create a beautiful persimmon.  Amaco's colors are so stable, and true to the color on their test tiles, that they can be used in a very painterly way.  The only ones that still give me problems are the greens  and very pastel blues and grays.  If you want a lighter color, white is probably not your best choice.  Want to lighten a red?  Try adding yellow with a tiny touch of white (unless you want pink)  Want to darken a red? try green with a tiny touch of black.

 

Regardless of whether you paint on bone dry (as I do) or bisque, another firing at cone 06 is wise.  I've never had underglazes run if the ware has been fired after application.

 

Shirley

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