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Briana

Drying Pots developing mold?

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Hello all. So I seem to have run into a problem when drying clay to leatherhard. It looks like on some pots there’s a mold layer developing on the bottom. I’ve include photos for reference. 

My current process is as follows:

Throwing with minimal water on wooden bats when I can, ensuring that I dry pots as much as possible.

Drying on the wooden bats, or removing the item from the wooden bats and placing clay pots on a thin sheet of plywood placed on top of a dresser.  The throwing area and drying area are both in my office, inside. The A/C has been off this week and the climate is a bit muggy (I’m in Florida), but its not unbearable. The “drying time” to leatherhard was about 36 hours. 

Has this happened to anyone else? If so, how did you nip the issue in the butt. It’s not something I’m thrilled about at the moment. 

F5F64158-9629-4579-938A-4D12B83D407A.jpeg

Edited by Briana

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I haven't had mold like that on the bottoms of my pots, but I do get moldy smells in my throwing water and recycling bucket during the summer months. Mold is generally not considered a big deal in a pottery studio. Hard to avoid with all the moist materials. 36 hours to leatherhard means your environment in very humid, so the mold is not surprising. I wouldn't worry about it!

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There is usually mold on the fresh bags of clay, when I open them up.  It grosses my students out, but I simply explain to them, that their hands are probably dirtier, than the clay...

The mold on the clay is either white or black.  Usually, if it shows up on the wares/ projects, it's only if they sit awhile.  The ware boards are worse, since they don't always have a chance to dry out, as they are constantly being used.  On those, it's usually a blackish mold.  

No matter the case, I never worry about it.  On the projects, the kiln will take care of the mold, and on the boards, a little soap and water is adequate.  

The biggest issue is the bacteria that likes to eat the binder in the underglazes.  As the saying goes, the smell of those could knock a buzzard off a manure wagon...

D.M.Ernst and Babs like this

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Okay, so now I am curious? Does your throwing water or pieces shown have the classic mold smell?  High organic content ball clay would produce this kind of mold, but the body is usually much darker. This does remind me of soluble salt migration as well.  

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From stories i've heard a good bag of mody clay is like finding a wheel of nicely ripened cheese - the more mold/smell the better. I wonder now if the green i've seen is strictly mold. Some old bags i've found look like little forests of growth.

Mold on pots in something different i suspect.

I know a 10% bleach solution in a spray bottle is recommended for black mold so maybe a bleach solution might work.

I recycle my throwing water----> slop bucket----> throwing water so a bit of bleach helps keep the swamp aroma to a minimum. I'm using tea tree in a small slip container at the moment for a more fragrant option. I imagine oil of oregano will work the same to keep the bacteria(?) from producing the swamp gases(sulphur/methane?).

Rae Reich likes this

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Guest JBaymore
31 minutes ago, glazenerd said:

 This does remind me of soluble salt migration as well.  

That is what my eyeballs went to from the picture also, Tom.

best,

................john

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6 hours ago, glazenerd said:

John: easy enough to test- couple of drops of vinegar that foams up- salts.

I’m curious about the salt migration...

 

this is the clay I’m currently using. 

https://www.highwaterclays.com/index.cfm?fuseaction=product.display&product_ID=5409&ParentCat=575

 

Also, no other mold showing up yet. No moldy smell or anything lurking in the slop buckets. If it’s expected, I’m less worried about it as the material is organic, however since the studio is inside my house right now, I’d rather avoid the mold if possible. I’m curious abiut mixing a little bleach into a spray bottle. Is that “safe” for the clay? And at what point do you actually intervene with the mold formation?

Edited by Briana

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I'm going to say it's probably not soluble salts because the pattern doesn't look like efflorescence.  It looks to me like you set the "moldy piece" on something.  Hence the ring shape, which is the portion of the piece which would be in direct contact with the board you set the piece on after throwing.

Mold would grow more randomly, and salt would effloresce in a different pattern (and would likely be a problem for all, not some).

My question:  when throwing, does this clay like to settle out in the slip bucket, maybe forming a hardpan at the bottom?

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3 hours ago, Briana said:

since the studio is inside my house right now, I’d rather avoid the mold if possible

Mold will grow anywhere that has moisture and something for the mold to eat, including in houses with no pottery studio. And it won't grow when those two things aren't present. So the mold in your studio doesn't automatically cause mold to grow elsewhere in your house. You should be more vigilant about not spreading dust into your living space. Dust will easily travel without you trying. There should be a door between your pottery space and your living space. And use dedicated studio shoes, that you put on and take off inside your studio. My studio is in my basement, and I leave the shoes at the bottom of the stairs. Dust and the summer mold never reaches the first floor. Even when the mold gets smelly I don't smell it from the first floor. 

Edited by GEP
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Third Highwater clay issue in a month. Since you are using a white stoneware body,  even more prone to believe it is soluble salts. The lack of mold smell in your throwing water is also telling. Made a prediction in another thread recently that clay issues would out pace glaze issues in the years to come- perhaps sooner than I expected. Someone at Highwater needs to do some batch testing.

by chance was this clay wetter than normal? Tacky? 

Nerd

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3 hours ago, glazenerd said:

Third Highwater clay issue in a month. Since you are using a white stoneware body,  even more prone to believe it is soluble salts. The lack of mold smell in your throwing water is also telling. Made a prediction in another thread recently that clay issues would out pace glaze issues in the years to come- perhaps sooner than I expected. Someone at Highwater needs to do some batch testing.

by chance was this clay wetter than normal? Tacky? 

Nerd

The clay is rather moist & tacky compared to others I’ve used when taking a class at a local art school. Otherwise, it’s the first “at home” clay I’ve used. I have another type that I haven’t broken into yet. 

7 hours ago, Tyler Miller said:

I'm going to say it's probably not soluble salts because the pattern doesn't look like efflorescence.  It looks to me like you set the "moldy piece" on something.  Hence the ring shape, which is the portion of the piece which would be in direct contact with the board you set the piece on after throwing.

Mold would grow more randomly, and salt would effloresce in a different pattern (and would likely be a problem for all, not some).

My question:  when throwing, does this clay like to settle out in the slip bucket, maybe forming a hardpan at the bottom?

After throwing I do transfer my pieces to basically a piece of thin plywood for drying. And yes, the clay does settle out rather quickly. 

 

Also, I have been somewhat careful with the creation of dust and limiting the transmission into the rest of my living space, though to be honest I’m still also using the studio space as an office, so the lines are blurred. We’re in process of purchasing a home & hopefully I’ll have a dedicated studio space at that time. 

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Briana,

Since the clay does hardpan, here's my theory based on my own personal experience.  I throw a thixotropic (the more you touch it the softer/stickier it gets) cone 10 porcelain body that has given me similar residues on pots before.

What it turned out to be in my case was feldspar.  When this clay becomes slip, it doesn't like my hard water and settles out almost instantly.  Big ol' hardpan in my throwing slip bowl of flint and feldspar, with the kaolin/ball clay still in suspension.  It would settle out on my hands, and when I'd wipe them off, the feldspar/flint would be harder to get off.  I had a thumbprint of the exact appearance of your "mold" show up on a mug as it was drying.

Incidently, this clay body I used does effloresce a little soluble salt, but it's the tiniest amount and doesn't affect anything.

The tl;dr answer:  If it is mold, like everyone says, just do nothing.  Won't hurt a thing.  If it's what I say, a gentle wipe after trimming with a slightly damp sponge will remove the residue and shouldn't return after trimming (provided your boards and hands are clean).

Edited by Tyler Miller
clarity

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As a point of clarification and in defense of swampy clay the rotten egg smell is sulfur/methane which is produce from bacteria not mold.

A good example of these anaerobic/aerobic bacteria in action are Winogradsky columns. These columns are easy to make and show the distribution of organisms through a sample of 'swamp' depending on their need for oxygen.

If i remember correctly the purple, non-sulfur, photosynthetic bacteria are isolated and put in some health drinks.

I'm sure this is more than most wanted to know about hydrogen-sulfide gas(looked it up) but if you ever feel the need to grow a swamp-in-a-jar look up winogradsky columns. When i first found them I felt somehow let down we weren't required to make them in highschool biology class or even jr. high for that matter.

anyway

Edited by C.Banks

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8 hours ago, glazenerd said:

Someone at Highwater needs to do some batch testing.

If you feel confident that something needs to be tested, will you contact them yourself? 

Edit to add: I'm a little uncomfortable with this forum broadly blaming the manufacturer for a variety of anecdotal problems (which to some appear to be normal occurences rather than problems, and when a large sample of Hghwater clay users love the clays and have no complaints), without bringing the concerns directly to them and letting them respond. 

Edited by GEP

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Yes Mea, I will do exactly that. From the complaints that I have seen in the last month: sounds like a simple matter of too much water? However, the tacky/ sticky  reports relate to ball clay levels, or even perhaps a change in ball clay supply. Every clay supplier out there hits a bump in the road at some point- who hasn't? 

 

Mea: email sent with specific links to relative topics. 

Edited by glazenerd
Added info

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Thank you, glazenerd. Critiquing and questioning is not inherently bad, but speculation making conclusions without the full picture is bad. 

Can you do the forum a favor ... post the email you sent them in the thread titled "Highwater Clay Users" that oldlady started? Then post any response you get? It belongs there more than here in this thread about mold. And to me, oldlady is the only one having a legit problem with her clay, so any answers found should be for her. 

Edited by GEP

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