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Bisque Fired Underglaze Bleeding Under Transparent Glaze?

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I started pottery a bit over a year ago and recently begun exploring decorative techniques.

I tried some underglaze inlay on a greenware piece, carving out decorative lines on a small waxed porcelain cup, then painting the whole thing with blue underglaze, and wiping off the excess underglaze. I bisque fired the piece, then dipped it in transparent glaze and fired it again. The final cup has streaky underglaze, I don't understand why since the underglaze was bisque fired before I applied the final glaze? (I'll attach a picture, please note it's just a test piece :)

 

I do notice however that the streaking seems to occur on those lines that were less deep (the straight lines were carved a bit deeper into the clay, might that be the solution? - I thought mishima could be fairly superficial, am I wrong?)

 

Should I try to sponge on the clear glaze instead of dipping? Also, I find that dipping gives me a bit of a thick final transparent coating, could I try and brush it on in order to obtain a thinner coating or am I just setting myself up for a huge mess? 

I'd very much appreciate some experienced insight on this! Many Thanks in advance! 

 

 

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Well I don't know your firing temp but I fire to cone 10 and use underglazes with clear over without issues.

 

However, I used underglazes in Raku with a clear (80-20) over it and the underglazes ran, even though it was only fired to cone 06. I suspect that my clear glaze, which is 80 percent gherstly borate, a powerful flux agent, caused the underglaze to run because of the high amount of flux.  You might consider the ingredients in your clear glaze and the firing temperature.

 

This is all supposition but something to think about.  GL.  Rakuku

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Might your underglaze not be applied evenly?  If so,  the streaking may be caused by uneven layers of underglaze.  Remember to apply more than one layer of underglaze (painted on in various directions).

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A picture would really help ... can you try to attach one? There are just so many possible reasons.

 

 

I thought I had inserted the pic in my post but for some reason, it's not there (tried again now, still nothing, maybe some restriction due to the fact I'm a new user on this forum?), however, this is a link: 

http://www.cavolettodibruxelles.it/wp-content/uploads/2017/03/IMG_7304.jpg

Hope this helps, and think you for your time! :)

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Might your underglaze not be applied evenly?  If so,  the streaking may be caused by uneven layers of underglaze.  Remember to apply more than one layer of underglaze (painted on in various directions).

 

The underglaze went only into the groves I traced into the dry pot, everything else was wiped of. Should I still apply several layers? 

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Well I don't know your firing temp but I fire to cone 10 and use underglazes with clear over without issues.

 

However, I used underglazes in Raku with a clear (80-20) over it and the underglazes ran, even though it was only fired to cone 06. I suspect that my clear glaze, which is 80 percent gherstly borate, a powerful flux agent, caused the underglaze to run because of the high amount of flux.  You might consider the ingredients in your clear glaze and the firing temperature.

 

This is all supposition but something to think about.  GL.  Rakuku

 

I'll ask! I use a shared studio so I don't get to handle the kiln (it fires at cone 6 but that's all I know), and I have no idea about the ingredients in the clear glaze (it's made in the studio, I'll ask!). In case the percentage of gherstly borate would be high, should I look up another clear glaze? Suggestions? Also: could this be due to a too thick layer of glaze? - this clear coating was too thick imho. 

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That is pretty! Truthfully, I think it adds more visual interest to have your underglaze slightly dissolved like that, than having a "candy apple" coating that just sits on top of your decoration.

 

As to what's going on technically:

Theres nothing wrong with your glaze application, and sponging it on won't change this effect. There's nothing wrong with your Mishima technique, either.

Your clear glaze is fluid, as Neil suggested, and it's dissolving your underglaze a bit, and running. This glaze is likely forgiving in its application, as it smooths out and doesn't show any application lines, but I'm betting you have to be mindful of how far up from the bottom of the pot you apply it. Likely the glaze is low in alumina, and high in whatever flux it uses possibly boron from Gerstley borate, but could be sodium too. It may be prone to crazing, if it's actually a glaze that's meant to be used at lower temperatures, or just plain unbalanced. If you can get the recipe from your studio, one of us may be able to run it through glaze software for you and see. We can go from there once we know what's going on.

 

Or you could play with the effect intentionally. If that's the case, I'd do some testing to see how durable the glaze is. If a glaze doesn't have enough alumina in it, it can run in the kiln or be a soft glass that etches easily, or dissolves, or leaches. Bad things if you're making food wares.

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aaah that darn cobalt.

 

the problem is not the glaze. it is the underglaze.

 

what is your underglaze? made in a studio? store bought?

 

i have used Amaco's jet black V-361 underglaze. never had an issue of bleeding lines on greenware or bisqueware. actually any underglaze or slip without cobalt i have had no problem with bleed. 

 

have used mason stain black slip (NOT cobalt free) drowned in clear glaze. ooooh. lots of bleeds just like yours. however it looks really cool so i've manipulated to purposely get the bleed. 

 

IF you look at the masters doing buncheong/mishima - you will see they use black and white clay. you dont really see colour. hmm!!!! wonder why? perhaps to make work easier. 

 

my favourite - using red clay using white slip. and trying different colour transparent glazes. just some other options.

 

to truly get what you want - the only way i have succeeded is by using cobalt oxide directly on top of clear glaze. i've never succeeded bleedless under the glaze.

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I really like the bleeds & am trying to obtain that but so far no success! Go figure! I tried adding some cobalt oxide to my black underglaze & used a clear glaze that was suppose to make it run. Alas no! Nothing ran. Any helps would be appreciated as well.

I do really like the pot you share a picture of. Wish I was getting that result. Thanks everyone

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1 hour ago, Jackfish jo said:

I really like the bleeds & am trying to obtain that but so far no success! Go figure! I tried adding some cobalt oxide to my black underglaze & used a clear glaze that was suppose to make it run. Alas no! Nothing ran. Any helps would be appreciated as well.

I do really like the pot you share a picture of. Wish I was getting that result. Thanks everyone

Make your glaze more fluid by adjusting the recipe, or fire hotter.

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1 hour ago, Jackfish jo said:

I really like the bleeds & am trying to obtain that but so far no success! Go figure! I tried adding some cobalt oxide to my black underglaze & used a clear glaze that was suppose to make it run. Alas no! Nothing ran. Any helps would be appreciated as well.

I do really like the pot you share a picture of. Wish I was getting that result. Thanks everyone

There was a thread on this recently here. Try a more fluid glaze and the underglaze should run.

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