Yixing

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Youzi
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Mon Jul 19, 2021 10:46 am

Bok wrote:
Sun Jul 18, 2021 8:03 pm
Another thing on my mind recently is what I used to distinguish as “Wuni” and “Whuhuini” in the past. These two differently used terms had been given to me by more experienced collectors and Yixing experts.

Whuhuini explained as ash covered reduction firing, Wuni as a considerably less defined “also-dark-grey-reduction-fired-but-different” category. I did not question this at the time, but in hindsight it does not make any sense.

_For one: why would they go through the trouble to cover some in ash and others not?
_It does not sound like something Yixing potters would do, randomness and imperfection were not sought after. They took great care as to that pieces did not have random firing effects happen.
_there are seemingly no written sources on either one of those methods, as far as I am aware.

From my observations and from handling dozens of these grey pieces I have come to the conclusion that it is much simpler than that: Reduction fired, full stop.

The difference in colour simply explained by the different underlying clay at the base. Duanni for example usually results in a yellowish grey that sometimes can appear dark olive green or brownish grey. Other clays like Zisha ends up more dark blueish grey.

Further evidenced by the fact that the supposedly Zisha reduction still shows the silvery mica spots, while the green ones do not.

All this to say, apologies if I furthered this confusing and possibly not correct terminology of Wuni and Wuhuini by referencing it in the past. Personally I will only be using reduction fired from now on.
From what I gathered this my understanding of the black pots:

All black / grey pots are reduction fired or dosed with manganese oxide in later F1.

Wuni is an actual ore, which is black, dark gray, hence the name 乌泥.

Wuhui 捂灰 or wuhuini 捂灰泥. Is a reduction fired teapot, using the ancient ash firing technique. Which was a uniquely developed technique to reduction fire teapots in an oxidative kiln environment. It was initially / usually done to cover firing previous firing flaws, like efflorescence or fire marks.

Then there was also "real" Heini. Which is reduction firing in the modern sense, as the kiln it self was in a reduction state. It either happend accidentally or intentionally. These are more black, dark than the Ash fired counterparts, not so much grey. Those pots are extremely rare, due to the knowledge not being available. They are usually high iron zini / hongni teapots. Nothing "magical" or legendary clay.

Then an exemption, but often confused with the previous three is Qinghuini. Which is a special kind of grey brown zini. If I remember correctly those have naturally higher manganese content which gives them the greyish tone in oxidative firing.
Last edited by Youzi on Mon Jul 19, 2021 12:17 pm, edited 1 time in total.
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Bok
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Mon Jul 19, 2021 11:11 am

@Youzi thanks for chiming in. Makes sense.

Still doesn’t feel like the whole picture to me. In regards to old pots the dark grey, be they lighter green grey or dark blue grey, both happen mostly on heart sutra Julunzhu, so a very specific design, which for me would exclude the explanation of covering up damages. Usually either black or normal Duanni in what feels like 80% of cases, with some lesser seen brown Zisha ones. Other clays mostly with unadorned Julunzhu only.

Some may look black, but it’s mostly patina, when cleaned it’s always a closer to mid-dark grey. I’ve never seen anything old that was truly dark like the later coloured factory Heini.

Some light shed, but it remains inconclusive to me for now.
Mark-S
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Mon Jul 19, 2021 11:17 am

OCTO wrote:
Mon Jul 19, 2021 10:41 am
It’s a teapet 😃😃
Cute :D
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wave_code
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Mon Jul 19, 2021 11:45 am

@OCTO was offering me some helpful guidance on some pots recently, including clarifying a bit for me about reduction fire how you can usually still see the under-color of something coming through in the right light.

The fact that my 90s pot that I thought was black from reduction fire is really more of a jet black makes me think that either it has oxide added clay and/or maybe still reduction or... are these types of pots a totally different type of ore, maybe not even from the same region? I sort of assumed it was reduction fired zini, but maybe its way off. It certainly has a different effect than my other zini, gives everything I put in it a little more bite. I've seen them mostly referred to as "black iron sand" rather than "purple sand" which makes me wonder are these even technically yixing ore? or is that a fancy way of saying 'yixing clay with additives'.

@Bok since you have quite a mix of clays, do you feel like all the reduction pots are hard to pair just each due to individual character, or do you find they all wind up behaving pretty similarly regardless of what the clay was? I'm wondering what actual chemical/structural change occurs in the clays that makes them much more 'picky'.
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Youzi
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Mon Jul 19, 2021 12:16 pm

Bok wrote:
Mon Jul 19, 2021 11:11 am
Youzi thanks for chiming in. Makes sense.

Still doesn’t feel like the whole picture to me. In regards to old pots the dark grey, be they lighter green grey or dark blue grey, both happen mostly on heart sutra Julunzhu, so a very specific design, which for me would exclude the explanation of covering up damages. Usually either black or normal Duanni in what feels like 80% of cases, with some lesser seen brown Zisha ones. Other clays mostly with unadorned Julunzhu only.

Some may look black, but it’s mostly patina, when cleaned it’s always a closer to mid-dark grey. I’ve never seen anything old that was truly dark like the later coloured factory Heini.

Some light shed, but it remains inconclusive to me for now.
Which part is not clear? Just because the technique was used for covering up faults, doesn't mean it couldn't be used intentionally.

I indeed left out a "usually" from my statement. There are always exceptions to everything.
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Bok
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Mon Jul 19, 2021 8:06 pm

@Youzi you’re right, the technique is clear.

For me the actual circumstances at the time are still less so, due to lack of sources on the topic.

Did I remember this wrong or is Wuni actually really(really extinct this time) rare? Or not usable in pure form? I can not recall ever seeing one old or new.
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Bok
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Mon Jul 19, 2021 8:09 pm

wave_code wrote:
Mon Jul 19, 2021 11:45 am
Bok since you have quite a mix of clays, do you feel like all the reduction pots are hard to pair just each due to individual character, or do you find they all wind up behaving pretty similarly regardless of what the clay was? I'm wondering what actual chemical/structural change occurs in the clays that makes them much more 'picky'.
hard to say, as sizes, thickness and shape vary a bit, so other factors may be at play. Just the general, unsubstantiated impression that they often > only < work with Puerh and are more hit than miss with most other teas.
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Youzi
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Tue Jul 20, 2021 9:31 am

Bok wrote:
Mon Jul 19, 2021 8:06 pm
Youzi you’re right, the technique is clear.

For me the actual circumstances at the time are still less so, due to lack of sources on the topic.

Did I remember this wrong or is Wuni actually really(really extinct this time) rare? Or not usable in pure form? I can not recall ever seeing one old or new.
Well yeah, wuni is rare. But it isn't anything special. It's in the upper ore layer. And was used together with Jiani to make everyday pottery, containers and molds due to low shrinkage and high firing temperature requirement.

The colors are kinda lackluster, -ish colors. So light orangish borownish, dirty yellowish beige, etc. Sometimes was used for low end pots mixed with other cheap ores, if they didn't wanted to use zisha.
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Bok
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Tue Jul 20, 2021 9:46 am

@Youzi thanks for elaborating on that!
teabug
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Tue Jul 20, 2021 2:31 pm

Stupid question: does the shaping effect clay has on the brew, wear off after a couple of years of usage? So, does for instance the muting effect of a Zini pot become less pronounced when it has been used for say 300 times? Surely, the effect of the clay has to wane over time, right? Either due to mineral depletion of the surface area and/or due to limescale. Or is the mineral usage so minimal, that there is no effect of depletion noticable over time? In that case we only have limescale that hamper the interaction of the water with the clay.
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steanze
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Tue Jul 20, 2021 4:16 pm

teabug wrote:
Tue Jul 20, 2021 2:31 pm
Stupid question: does the shaping effect clay has on the brew, wear off after a couple of years of usage? So, does for instance the muting effect of a Zini pot become less pronounced when it has been used for say 300 times? Surely, the effect of the clay has to wane over time, right? Either due to mineral depletion of the surface area and/or due to limescale. Or is the mineral usage so minimal, that there is no effect of depletion noticable over time? In that case we only have limescale that hamper the interaction of the water with the clay.
The effect is not really due to minerals in the pot dissolving in the tea, but rather to tea being trapped in the pores. Mineral depletion is not an issue. If you use very hard water, and have a lot of calcium deposit, that might affect the performance of a pot.
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Baisao
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Tue Jul 20, 2021 8:37 pm

teabug wrote:
Tue Jul 20, 2021 2:31 pm
Stupid question: does the shaping effect clay has on the brew, wear off after a couple of years of usage? So, does for instance the muting effect of a Zini pot become less pronounced when it has been used for say 300 times? Surely, the effect of the clay has to wane over time, right? Either due to mineral depletion of the surface area and/or due to limescale. Or is the mineral usage so minimal, that there is no effect of depletion noticable over time? In that case we only have limescale that hamper the interaction of the water with the clay.
It’s an old tale that the change is caused by tea that has soaked into the pores of the clay. It’s too simplistic an explanation and isn’t an observable fact.

We know that porosity has little to do with the effect of clays on tea because the expected effects correlate poorly with how porous a clay actually is. There are other things involved here that need to be studied that will fall into the category of surface chemistry.

@LeoFox has posted a nice study on this and we talk briefly about surface chemistry here: viewtopic.php?p=37061#p37061

Additionally, apart from outliers, most Yixing are not porous enough to absorb tea to any significant degree.

There are some clays that weep and will absorb tea over time but these are exceptions and often the result of poor firing.

A frequently used pot will change over time as the clay surface is covered in a waxy substance (fatty acids, etc.) that is deposited with each tea session. This is easily observed given a little time and happens even if you rinse well with hot water after completing each tea session. This is a coating and not tea that has soaked into the pores of clay. This waxy substance changes the surface chemistry of the pot over time.

The lore is that this coating (aka, seasoning) is good for tea. It certainly makes Yixing pots more attractive!

However, this waxy substance comes with some issues.

There’s been some evidence posted by @pedant that indicates that this waxy substance may be bad for health even in small amounts (link below). It may be bad for tea for various reasons. The issue I have with it is that it is covering, and therefore altering the effects of the clay I invested in.

This is why I have started resetting pots that I’ve used for almost two decades and plan to reset them regularly. No harm has been done to the pots and the characteristics that I fell in love with have now returned.

More here: viewtopic.php?p=20633#p20633

Pedants post on these fatty acids: viewtopic.php?p=4230#p4230
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wave_code
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Wed Jul 21, 2021 5:47 am

I have a few new pots on the way in 4 very different types of clay from different time periods/grades, so it will be interesting to see how they all behave initially and how they 'season' or not over time in parallel. I am getting the feeling more and more that a lot of things around seasoning and muting properties of certain (not all!) clays carries over from when production was very different- different ore, processing, and as @Baisao points out (and maybe most importantly?), firing. With the exception of one pot so far I've found most of my modern pots behave more or less the same very quickly - some slight changes here or there but nothing incredibly drastic. This includes pots that I thought were really robbing the tea of character because they were unseasoned- one year on and they still absolutely wreck certain teas - its clearly wasn't the lack of seasoning, it just how the clay is. A couple took a little bit of use, but within about a week I had a pretty accurate impression of how they were going to continue to behave. And even thenI still wonder how much of that was just my palette adjusting - thinking a pot was 'muting' something when maybe it was just highlighting something else or wasn't that I was used to in a particular tea so I attributed that to being a lack of seasoning rather than just getting a different result or it not being the right pairing.

I'd even go so far as to say some of the denser/higher fired pots I've tried tasted worse as they 'seasoned' if I let it build up since its not like there were small pores slowly being blocked that would otherwise have maybe sucked oils or aroma from the tea, but was just getting a deposit of oils that could have slowly been turning rancid. I gave a stoneware pot a thorough loofah scrubbing recently and it tastes much better now. I don't have much experience yet with older and lower fired yixing, but I can say that the smell, porousness and behavior of an old Nixing pot compared to a modern one is very different - it is significantly more muting, and has become less so as I put a lot of seasoning into it, but my modern one which is much denser and higher fired has brewed more or less the same from day one. So maybe it is particularly with some pots, especially older or under-fired ones effects like muting might become a bit less over time, but I'm sure you still cross a threshold at some point where you are just making a gross build-up inside your pot. Just like with the need to boil to 'open up' new pots this seems more and more to me like a lot of it is falling into the 'tea lore' category where things are still repeated as some sort of common fact despite circumstances having changed drastically around what a thing is - cultivars and processing of tea has changed, most of us aren't using boiled stream or natural spring water, and most of us aren't using 100+ year old pots so why would we expect all those things to still function like if we were making tea 100 years ago.
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LeoFox
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Wed Jul 21, 2021 6:52 am

"Seasoning" is very complex. The paper referred to by baisao reports on the mass spec analysis of the waxy "shiny" exterior of 2 pots. The "wax" was extracted by acetone. The results mainly point to the identification of fatty acids that are also found in oxidized tea.

This is from the paper. You can see the pots they used and the before and after pics of the acetone extraction
This is from the paper. You can see the pots they used and the before and after pics of the acetone extraction
signal-2021-07-20-224029.jpg (80.99 KiB) Viewed 3694 times

As for the interior of the pot, the paper suggests without experimental evidence that they may be mostly complex aggregates of polyphenols and calcium-though is likely the waxy fatty acids are also present. The statement about the interior is inferred from very old papers on the composition of tea scum. In any case, the composition of seasoning is likely to be highly heterogeneous and dynamic over time. I imagine the quality of the seasoning depends on the quality of the tea. A smoky tea can make a smoky pot. A stinky pu can make a stinky pot.

How does clay impact tea and how is this "impact" influenced by the heterogenous fatty acids and polyphenol aggregates? I am sure this would take a lot of study. But who would fund this kind of study?
olivierd
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Wed Jul 21, 2021 7:55 am

LeoFox wrote:
Wed Jul 21, 2021 6:52 am
I am sure this would take a lot of study. But who would fund this kind of study?
A small contribution you might already know :
https://www.researchgate.net/profile/Ja ... usions.pdf
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