Show Off Your Pots and Cups XV

[MarshalN]

Hmm, I wonder what the white stuff is then

[entropyembrace]

Hmm, I wonder what the white stuff is then

I´m wondering that too....it has no odour and it has the same texture as the dark parts of the pot...just a dry, smooth texture I´d expect an unglazed pot with no rough particles in the clay to have.

It´s not fused to the clay body...it can be rubbed off with a fingernail...bu I havent worried about it too much since there´s none inside of the pot. It comes off as a light grey powder...

I may take a toothbrush to it and see how it looks if I take it all off even I don´t think it´s hurting the tea inside any.

[GreenwoodStudio]

It's hard to tell from the picture, but is this pot glazed or is it more of a burnished surface. If it's not glazed it could be something called scumming. Clays contain small amounts of soluble salts that will come to the surface as water within the the clay evaporates off. If it is glazed, it might be the break down of the glaze itself, if that glaze is say an unstable high alkaline glaze. Those are my guesses

Also, I'm wondering if the residue has a purple tinge to it? On my screen it does...

[TIM]

Hmm, I wonder what the white stuff is then

I would definitely be caution on this one.

[iannon]

Really cool looking pot tho..i think

[nickE]

Really cool looking pot tho..i think

+1

[entropyembrace]

It's hard to tell from the picture, but is this pot glazed or is it more of a burnished surface. If it's not glazed it could be something called scumming. Clays contain small amounts of soluble salts that will come to the surface as water within the the clay evaporates off. If it is glazed, it might be the break down of the glaze itself, if that glaze is say an unstable high alkaline glaze. Those are my guesses

Also, I'm wondering if the residue has a purple tinge to it? On my screen it does...

Theres no glaze...it could definitely be scumming now that you mention it...and yes the residue is slightly purple. I´ve done a little bit of pottery and some of my pieces have scumming...but they were all white clay so it never looked dramatic like this is why I´d never thought of it.

My impression of the piece from first seeing it was that it wasn´t cleaned after coming out from the kiln...the white deposits being scumming would make sense.

[GreenwoodStudio]

Well, I don't want to be an alarmist, BUT my first thought looking at this piece was that the clay was loaded with Manganese to give it the dark color, and the purple color would be another clue pointing to Manganese used as a colorant. I personally would not use this piece more until you find out more about how it. Better to be safe. Manganese is VERY bad for you and you would not want to be ingesting it! Do a google search.

[JeiKun4114]

My newly acquired Petr Novak cups His wares are worth the wait

[entropyembrace]

Well, I don't want to be an alarmist, BUT my first thought looking at this piece was that the clay was loaded with Manganese to give it the dark color, and the purple color would be another clue pointing to Manganese used as a colorant. I personally would not use this piece more until you find out more about how it. Better to be safe. Manganese is VERY bad for you and you would not want to be ingesting it! Do a google search.

It´s an essential nutrient required for proper bone formation, nervous system function and hormone synthesis.

But it´s also a serious danger to ceramics workers when large quantities of manganese dust are inhaled. It generally has very poor absorption through the GI system and usually isn´t dangerous when ingested except in extremely high doses.

Most sources I´m seeing indicate that in functional pieces the exposure to manganese isn´t dangerous...the question that comes up is...there´s no real concept of unglazed pieces as being functional in western ceramics so it´s hard to find good information about their safety in English.

I wouldnt be comfortable using it if the white scumming or whatever it is was on the inside...but it´s external only...and even what I can probably remove all or most of it if I work at it a bit. I´m reasonably sure not very much is leaching from the inside of the pot....it just doesn´t affect taste enough to be adding lots of mineral ions to the water.

[MarshalN]

There's also the possibility that the white stuff is coming from your water leaving residue on the surface. I've had that happen to me once when I was in Beijing, but that should be more easily removable than what I'm seeing here.

[GreenwoodStudio]

Well as long as you comfortable with the current research, your guess at what levels and forms of the compound (which seem pretty obviously soluble) you might be ingesting based on taste and the theory that it's only going to leach out in one direction through the claybody, then by all means enjoy your teapot.

[entropyembrace]

Well as long as you comfortable with the current research, your guess at what levels and forms of the compound (which seem pretty obviously soluble) you might be ingesting based on taste and the theory that it's only going to leach out in one direction through the claybody, then by all means enjoy your teapot.

I´m basing it more on the fact that there are very few cases oral ingestion of manganese leading to poisining, and that the acceptable daily intake of manganese is quite high (10-11mg) If 10mg of manganese were leaching out of the pot each session that would be easily apparent.

[hopeofdawn]

My newly acquired Petr Novak cups His wares are worth the wait

Wow, both of those are so dramatic--love the sweep of the brushed on slip on the first, and the warm colors of the body on the second.

[JeiKun4114]

My newly acquired Petr Novak cups His wares are worth the wait

Wow, both of those are so dramatic--love the sweep of the brushed on slip on the first, and the warm colors of the body on the second.

Thanks hopeofdawn