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Black Coring / Black Bone Syndrome (BBS), reduction firing
Posted: Sat Aug 24, 2019 7:52 am
by pedant
continuing from
here, i wanted to share some more info about Black Bone Syndrome (BBS) and discuss.
first, some info from
@peacener (shared with me elsewhere):
peacener wrote:
BBS (black bone syndrome) as someone pointed out to me... is good for tea, specifically, aged tea. The kiln change happened in old dragon kilns and also happened to jianyao teabowls also fired in dragon kilns. It would convert the Iron Fe
2O
3 to iron magnetite Fe
3O
4. I have shared my teabowl and both of my zhuni pots that exhibit this characteristic.
old zhuni has a high iron content to begin with. so did the clay for the (song dynasty) jianyao teabowls. Once you dive deeper into the mysteries of zhuni and jianyao, you see how similar their firing is and how the clay has similar reduction fired color change (greyish) all simply because the clay for jianyao bowls and zhuni have such a high iron content. And if jian bowl and zhuni are fired perfectly, also exhibit similar color, of course zhuni being more red, and Jian being an off reddish-brown. It is worthy of notation though that they were both fired for a lengthy duration (2 weeks?) at a similar temperature (1200c), too, and both, as I repeat myself, in dragon kilns. dragon kilns are seriously cool. epsilon phase iron oxides and dragon kilns are something to really love!
https://ceramics.org/tag/epsilon-phase-iron-oxide
so. similarly, magnetism is present on both the left objects (clay), whereas magnetism is absent on the right objects (clay):
- peacener_BBS.jpg (235.51 KiB) Viewed 11372 times
here's a video also from
@peacener of a laozhuni pot (same pot as in the lower left pane of the pic above) exhibiting ferromagnetism:
the ovoid object dragging the lid around is a magnet.
and here's a shot of its interior:
- peacener_BBS2.jpg (48.88 KiB) Viewed 11372 times
Re: Black Bone Syndrome (BBS), reduction firing
Posted: Sat Aug 24, 2019 8:35 am
by Bok
Nice one! Thanks for setting that up.
One thing I would like to add: optics are deceiving, in regards to the side by side comparison of the teapot lids. It can be very obvious visually like in these examples, or have a chip so, you can actually see the black inside, as on mine - but it can also look just like any other Hongni, Zhuni, Zini.
I have seen a few in person which did not give away any clues, unless tested with a magnet.
So, visual marks are proof, but the absence of them is not proof of the opposite.
Re: Black Bone Syndrome (BBS), reduction firing
Posted: Mon Aug 26, 2019 12:04 am
by pedant
a bit more:
peacener wrote:
Jianyao bowl also has BBS which I did not formerly state. So that grey skin breaks, behind it you will find black. I have seen examples of partial bowls and shards.
I've attached a video and go ahead and share if you want. I use small rare earth magnets that weigh similar weights to test to make sure the ferromagnetism is the same/similar thruout (rim and foot) as to eradicate idea of rebuilt body on old song foot*.
*sometimes, modern tea bowls are built upon authentic song dynasty feet. for example, this could be a method of forgery to defeat thermoluminescence dating.
it's a pretty unscientific test. a stack of tiny rare earth magnets adhering to both parts of the bowl. maybe interesting nonetheless:
Re: Black Bone Syndrome (BBS), reduction firing
Posted: Mon Aug 26, 2019 1:03 pm
by .m.
This is an awesome topic. Thanks for sharing.
Do or can zini pots exhibit BBS? (I've seen some pictures of old pots that were black at a chip, but it wasn't clear if it is a BBS or a dirt).
Also, weren't all qing/ROC pots fired in a dragon kiln? I imagine that it is not just about the dragon kiln and the amount of iron in the clay, but also about the way the kiln was fired and the specific conditions that arised within the kiln.
Re: Black Bone Syndrome (BBS), reduction firing
Posted: Mon Aug 26, 2019 7:48 pm
by Bok
Yes, it can happen with Zini as well. Harder to detect due to the overall darker tone of the clay.
I think placement in the kiln also plays a role. Don’t forget that there were more kilns in ancient China than the imperial dragon kiln, lots of smaller workshops just like today, who knows how they fired in what kilns...
Re: Black Bone Syndrome (BBS), reduction firing
Posted: Fri Aug 28, 2020 1:12 pm
by Youzi
Re: Black Bone Syndrome (BBS), reduction firing
Posted: Fri Aug 28, 2020 7:01 pm
by Bok
@Youzi seems indeed to be the same thing, thanks! Not sure how it would change for the dragon kiln as there is no bisque firing.
Re: Black Bone Syndrome (BBS), reduction firing
Posted: Sat Aug 29, 2020 1:02 pm
by Youzi
Bok wrote: ↑Fri Aug 28, 2020 7:01 pm
Youzi seems indeed to be the same thing, thanks! Not sure how it would change for the dragon kiln as there is no bisque firing.
There are no need for bisque firing, because the kiln is slowly heated up, then also cooled down, or in this case not slow enough, because Zhuni needs a slower heat up and cool down than normal zisha. Basically it seems Black Bone is a consequence of Zhuni fired together with other Zisha, therefore the ramp up/down phase not adjusted, and the Constant changing of the Dragon Kiln between Oxidation and reduction firing.
Re: Black Bone Syndrome (BBS), reduction firing
Posted: Sun Aug 30, 2020 7:18 pm
by TeaTotaling
Upon testing my antique Zhuni with a refrigerator magnet, the lid does exhibit magnetism! I have noticed the lid feels heavy, as well. It weighs almost 32 grams. The magnet I used was kind of wonky, I don't have any like the one's in the video above. I wasn't detecting any pull in body of the teapot.
@Bok regarding the Zhuni you recently posted, is the body of the pot magnetic, or just the lid?
Re: Black Bone Syndrome (BBS), reduction firing
Posted: Sun Aug 30, 2020 7:30 pm
by Bok
TeaTotaling wrote: ↑Sun Aug 30, 2020 7:18 pm
Upon testing my antique Zhuni with a refrigerator magnet, the lid does exhibit magnetism! I have noticed the lid feels heavy, as well. It weighs almost 32 grams. The magnet I used was kind of wonky, I don't have any like the one's in the video above. I wasn't detecting any pull in body of the teapot.
Bok regarding the Zhuni you recently posted, is the body of the pot magnetic, or just the lid?
Everything is. Inside out.
I got another where only the inside is a weakly magnetic. Heaviness has nothing to do with it by the way.
Congrats!
Re: Black Bone Syndrome (BBS), reduction firing
Posted: Mon Aug 31, 2020 12:29 pm
by TeaTotaling
Bok wrote: ↑Sun Aug 30, 2020 7:30 pm
TeaTotaling wrote: ↑Sun Aug 30, 2020 7:18 pm
Upon testing my antique Zhuni with a refrigerator magnet, the lid does exhibit magnetism! I have noticed the lid feels heavy, as well. It weighs almost 32 grams. The magnet I used was kind of wonky, I don't have any like the one's in the video above. I wasn't detecting any pull in body of the teapot.
Bok regarding the Zhuni you recently posted, is the body of the pot magnetic, or just the lid?
Everything is. Inside out.
I got another where only the inside is a weakly magnetic. Heaviness has nothing to do with it by the way.
Congrats!
Nice, thanks!
Regarding the weight of the lid, I was thinking the heaviness could potentially indicate a higher concentration of Fe.
Re: Black Bone Syndrome (BBS), reduction firing
Posted: Mon Aug 31, 2020 9:26 pm
by Bok
TeaTotaling wrote: ↑Mon Aug 31, 2020 12:29 pm
Regarding the weight of the lid, I was thinking the heaviness could potentially indicate a higher concentration of Fe.
I have handled a couple of this style and they all have a comparably heavy lid, seems to be the norm for these.
Re: Black Coring / Black Bone Syndrome (BBS), reduction firing
Posted: Tue Dec 13, 2022 10:38 pm
by LeoFox
It seems the entry on black coring has been updated
https://digitalfire.com/glossary/black+coring
Based on the update, black coring can strengthen fired clay - as long as feldspar is present - by vitrifying the body