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Kingram

Salt Effloresence On Glazed Pottery

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I have several pieces of pottery in an antique mall. Today, I found several pieces of my pottery had a white deposit on top of the glaze and even what appears to be under the glaze. I believe it is salt effloresence. These pieces have been at the antique mall for approximately 4 months...but the white deposit appeared just recently. It appeared to be under the glaze on one piece and is now pitting. Has anyone experienced? Any suggestions on how to avoid it?post-73804-0-16974900-1451947748_thumb.jpeg

post-73804-0-16974900-1451947748_thumb.jpeg

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See second page or so of attached.

 

http://www.mnhs.org/preserve/conservation/connectingmn/docs_pdfs/repurposedbook-ceramics_000.pdf

 

Likely that the salt was there in the clay body all along; it just took time to reach the surface or became exposed to conditions (humidity) that encouraged it to manifest itself.

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See second page or so of attached.http://www.mnhs.org/preserve/conservation/connectingmn/docs_pdfs/repurposedbook-ceramics_000.pdfLikely that the salt was there in the clay body all along; it just took time to reach the surface or became exposed to conditions (humidity) that encouraged it to manifest itself.

So they may have got the Mall vibe after all?

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I had a white deposit which showed up on top of a glaze after 2-3 days , can be wiped off but reappeared. People put it down to something emerging from the clay body. I also went a bit low on the firing on that particular. it was a copper coloured low fired glaze, same clay body as before with no white deposit... SO try firing a little higher nothing to lose..., is it only appearing under this glaze?

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 I would hazard a guess that there is no barium added to the clay you used or it is one made from clays with a high soluble salt content. By any chance did you use a low fire sculpture clay body? From digitalfire:

 

Barium carbonate is commonly added to clay bodies in small amounts (0.2-0.8%) to halt fired surface scumming or efflorescence It is slightly soluble in water and provides Ba++ ions to link with SO4-- ions in the water to form BaSO4 (barium sulfate). This new sulfate molecular form is much less soluble (2-3 mg/L), so it stays internal (rather than migrating to the surface during drying). However companies try minimize the use of barium (or even high clays with high soluble salts) because the barium sulphate generates sulphuric acid during firing and it corrodes kiln refractories. To get the best dissolution it is best to add the barium to the water first and mix as long as possible, then either add the water to the other dry ingredients (for plastic bodies) or add the other ingredients to the water (for slips).

 

I would try a different claybody.

bciskepottery likes this

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When I was making terra cotta, we used to always put in a scoop of Barium to "prevent scumming".

You can actually see this on some brick buildings.

Of course this only applies if you are mixing your own clay. I guess you could wedge some into your clay body BEFORE you start working with it.

TJR.

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I got a note and some photos from a customer this morning, regarding a salt-glazed wood-fired pot of mine:

 

 

"Hi Mea, I hope your holiday open house was a big success. You may remember me from all the wood-fired pieces that you've sold us over the years. Please help identify the white grainy powder sugar like substance with acidly odor (only up close) that keeps popping up on the wood fired elephant lid jar. It mostly appears on the textured, crackled, less glazed area. Please let me know how I can send you images if you think they would be helpful. Thanks."

 

 

Claybody is Highwater Phoenix, fired to cone 10 (give or take) in a wood kiln, right next to the firebox where it received heavy deposits of salt. I did not glaze the outside, that is just thick salt glaze. 

 

Is salt effloresence a reasonable explanation to give this customer? 

 

One last note ... the pot emerged from the wood kiln with a stress crack, which the customer knew about before buying. Therefore she knows it is for decorative use only, so I am not worried about poisoning her. 

 

 

 

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Does she live in an area of high humidity? Just that the prob glaze I mentioned above will do this if the item is out on the verandah for a time.. like for aplat pot holder.I live close to the coast, salt laden winds..

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She lives in my area (DC metro) which does get very humid in the summer. Though from the pictures she sent, it looks like she keeps the pot indoors.

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"Please help identify the white grainy powder sugar like substance with acidly odor (only up close) that keeps popping up on the wood fired elephant lid jar."

 

So, this was not there when you sold the pot, but has surfaced after?

 

Clayworks or Glen Echo? The salt chamber at Clayworks has a castable roof that is known to drop goobers during firing (a good reason to avoid the top shelf when loading).

 

Anything unusual in your liner glaze that could be working its way to the outside surface?

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"Please help identify the white grainy powder sugar like substance with acidly odor (only up close) that keeps popping up on the wood fired elephant lid jar."So, this was not there when you sold the pot, but has surfaced after?Clayworks or Glen Echo? The salt chamber at Clayworks has a castable roof that is known to drop goobers during firing (a good reason to avoid the top shelf when loading).Anything unusual in your liner glaze that could be working its way to the outside surface?

It surfaced after I sold the pot. And her note indicates she can remove it, but it keeps coming back.

 

This was fired at Clayworks. It was on the bottom shelf, and I am familiar with the roof goobers that can happen there, but this was definitely not the case this time.

 

The liner glaze was either a celadon or a shino, I don't remember (it was fired in 2013). Both glazes I've used many times, but this is the first report of this issue.

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GEP is it just on that one side of the pot, kinda looks like it??

I remember the pot has a really dark side, and a not so dark side. The difference is subtle, but I remember it. The photos show the white stuff on both sides.

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I wonder if the customer removes the white stuff by washing the pot? Thinking that water will dissolve the salts and if the pot is a bit porous salts in the water could be absorbed and then when the pot dries out the salts will remigrate back to the surface??? I wonder what would happen if she just brushed off the white deposits?

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"Please help identify the white grainy powder sugar like substance with acidly odor (only up close) that keeps popping up on the wood fired elephant lid jar."So, this was not there when you sold the pot, but has surfaced after?Clayworks or Glen Echo? The salt chamber at Clayworks has a castable roof that is known to drop goobers during firing (a good reason to avoid the top shelf when loading).Anything unusual in your liner glaze that could be working its way to the outside surface?

It surfaced after I sold the pot. And her note indicates she can remove it, but it keeps coming back.

 

This was fired at Clayworks. It was on the bottom shelf, and I am familiar with the roof goobers that can happen there, but this was definitely not the case this time.

 

The liner glaze was either a celadon or a shino, I don't remember (it was fired in 2013). Both glazes I've used many times, but this is the first report of this issue.

 

 

Clayworks uses both salt and soda in their firings.  Can't remember what is in the soda part, though. 

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I wonder if the customer removes the white stuff by washing the pot? Thinking that water will dissolve the salts and if the pot is a bit porous salts in the water could be absorbed and then when the pot dries out the salts will remigrate back to the surface??? I wonder what would happen if she just brushed off the white deposits?

I checked with my customer and she said:

 

"The amount of the substance on the jar is not as substantial as in the past; it reappears from time to time after I rubbed it off — it is a mystery."

 

So she is rubbing it off, rather than washing. And the problem has gotten better over time.

 

So, it sounds like no other wood/salt/soda firers out there have ever seen this before?

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I have never seen this in my salt pots-if the liner was a shino or celadon it should not matter.

I assume she (the customer is not using water in pot) Salt glaze surfaces are usually very hard when fired.Any chance this was fired in accord spot and not vitrified?

My only thought is the clay -with some sort of soluble ingredients .

I assume its not kept in a humid moldy environment ? and this is mold?

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Any chance this was fired in accord spot and not vitrified?

 

Yes, it was on a shelf that is known for being cool. 

 

I don't think it's mold. She said the texture is like sugar. And the photos show a nice clean kitchen in the background.

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