Yixing

[Baisao]

I'm pretty sure that Yixing does not vitrify which is the whole point since that's what allows the clay to have an effect on the water. Vitrification makes clay bodies impervious to water which is not the case with Yixing; Yixing is porous.

This is demonstrably false.

Please link something that speaks to Yixing being vitrified.

Edit: Vitrification is the clay pretty much becoming glass. Yixing does not do this. Or am I completely off base?

Properly fired Yixing is stoneware. Stoneware is considered fully vitrified. However, you can have a clay matrix that becomes vitrified but has interstitial spaces. These pots will not usually weep though there are some exceptions. An earthenware pot (not fully vitrified) will almost always weep. This weeping correlates to porousness.

Please search this thread for the week long discussion of porosity and surface chemistry. The effects of porosity are a myth.

[alejandro2high]

This is demonstrably false.

Please link something that speaks to Yixing being vitrified.

Edit: Vitrification is the clay pretty much becoming glass. Yixing does not do this. Or am I completely off base?

Properly fired Yixing is stoneware. Stoneware is considered fully vitrified. However, you can have a clay matrix that becomes vitrified but has interstitial spaces. These pots will not usually weep though there are some exceptions. An earthenware pot (not fully vitrified) will almost always weep. This weeping correlates to porousness.

Please search this thread for the week long discussion of porosity and surface chemistry. The effects of porosity are a myth.

But Yixing is fired at lower temperatures than other stoneware.

[Baisao]

Please link something that speaks to Yixing being vitrified.

Edit: Vitrification is the clay pretty much becoming glass. Yixing does not do this. Or am I completely off base?

Properly fired Yixing is stoneware. Stoneware is considered fully vitrified. However, you can have a clay matrix that becomes vitrified but has interstitial spaces. These pots will not usually weep though there are some exceptions. An earthenware pot (not fully vitrified) will almost always weep. This weeping correlates to porousness.

Please search this thread for the week long discussion of porosity and surface chemistry. The effects of porosity are a myth.

But Yixing is fired at lower temperatures than other stoneware.

Nevertheless it is stoneware* and vitrified. And even if it wasn’t, the porous argument is moot. See the earlier conversations re surface chemistry. This has been put to bed.

* I’d like to add that there is more involved than temperature, it is also a matter of time at a certain temperature. This is why pyrometric cones are used. So if someone says that a certain clay is only fired to 1280° F, that is only half of the story. We must ask how long was it at that temperature. These high temperatures were variable throughout a dragon kiln and the Yixing teapots were at high temps for days. Ideal conditions can be achieved today with the turn of a knob or push or a button, but it is still a matter of time and temperature.

[edit to clarify why temperature alone does not tell the whole story]

[Youzi]

I'm pretty sure that Yixing does not vitrify which is the whole point since that's what allows the clay to have an effect on the water. Vitrification makes clay bodies impervious to water which is not the case with Yixing; Yixing is porous.

This is demonstrably false.

Please link something that speaks to Yixing being vitrified.

Edit: Vitrification is the clay pretty much becoming glass. Yixing does not do this. Or am I completely off base?

Both of you are right. Yixing doesn't get vitrified. It gets sintered though. Which makes it impervious to water. In a high enough sintered state in which yixing is in. The clay particles are fused together, but There is still space between them, and the whole body is impervious to water.

You should imagine the impervious part of then inside of the teapot as a Mountain range with hills and valleys and some "caves" that don't run too deep.

Yixing is porous though. That can be easily measured and there's also a bunch of paper which measured the porosity of it. However it doesn't mean it's previous to water.

[alejandro2high]

This is demonstrably false.

Please link something that speaks to Yixing being vitrified.

Edit: Vitrification is the clay pretty much becoming glass. Yixing does not do this. Or am I completely off base?

Both of you are right. Yixing doesn't get vitrified. It gets sintered though. Which makes it impervious to water. In a high enough sintered state in which yixing is in. The clay particles are fused together, but There is still space between them, and the whole body is impervious to water.

You should imagine the impervious part of then inside of the teapot as a Mountain range with hills and valleys and some "caves" that don't run too deep.

Yixing is porous though. That can be easily measured and there's also a bunch of paper which measured the porosity of it. However it doesn't mean it's previous to water.

Thank you for clearing that up, Youzi!

[Baisao]

This is demonstrably false.

Please link something that speaks to Yixing being vitrified.

Edit: Vitrification is the clay pretty much becoming glass. Yixing does not do this. Or am I completely off base?

Both of you are right. Yixing doesn't get vitrified. It gets sintered though. Which makes it impervious to water. In a high enough sintered state in which yixing is in. The clay particles are fused together, but There is still space between them, and the whole body is impervious to water.

You should imagine the impervious part of then inside of the teapot as a Mountain range with hills and valleys and some "caves" that don't run too deep.

Yixing is porous though. That can be easily measured and there's also a bunch of paper which measured the porosity of it. However it doesn't mean it's previous to water.

The process as I understand it is that clay moves from being 1) dry clay --> 2) sintered --> 3) bisque --> 4) earthenware --> 5) stoneware. The bisque fired pots I've handled were still pretty "raw" and that is more fired than sintered. The particles in a sintered matrix are barely fused, IIRC. This is why I say that Yixing is vitrified. The particles have melted together and fused in the matrix, though not as much as some stoneware that forms a glass matrix.

I agree that it is a porous clay. The disagreement is that it is porousness that gives these clays their various characters. This is why I advised @alejandro2high to read the pages of discussion in this thread on surface chemistry vs porousness. The porousness theory doesn't map to real world experience. It is an overly simple explanation passed along as gospel by neophytes and sellers.

[alejandro2high]

Please link something that speaks to Yixing being vitrified.

Edit: Vitrification is the clay pretty much becoming glass. Yixing does not do this. Or am I completely off base?

Both of you are right. Yixing doesn't get vitrified. It gets sintered though. Which makes it impervious to water. In a high enough sintered state in which yixing is in. The clay particles are fused together, but There is still space between them, and the whole body is impervious to water.

You should imagine the impervious part of then inside of the teapot as a Mountain range with hills and valleys and some "caves" that don't run too deep.

Yixing is porous though. That can be easily measured and there's also a bunch of paper which measured the porosity of it. However it doesn't mean it's previous to water.

The process as I understand it is that clay moves from being 1) dry clay --> 2) sintered --> 3) bisque --> 4) earthenware --> 5) stoneware. The bisque fired pots I've handled were still pretty "raw" and that is more fired than sintered. The particles in a sintered matrix are barely fused, IIRC. This is why I say that Yixing is vitrified. The particles have melted together and fused in the matrix, though not as much as some stoneware that forms a glass matrix.

I agree that it is a porous clay. The disagreement is that it is porousness that gives these clays their various characters. This is why I advised alejandro2high to read the pages of discussion in this thread on surface chemistry vs porousness. The porousness theory doesn't map to real world experience. It is an overly simple explanation passed along as gospel by neophytes and sellers.

I just got done asking a potter, the dude from Bell Hill Pottery, and he also says that Yixing does it reach the point of vitrification.

And to clarify, I said that Yixing clay is not vitrified which is why it has an effect on the tea. I said that Yixing is porous, and I was using porous to mean the opposite of vitrified.

From what I read, it seems that you're saying that tea wax builds up inside the pot which is what is causing an effect, but I still don't think that is the case. If that was the case, new pots would all have either no effect or the same effect on tea which is not the case when you compare clays like zini and zhuni.

[Andrew S]

This might be a case where terms such as 'vitrification' and 'porosity' have different meanings within difference disciplines.

As a tea-drinker rather than a potter, ceramicist or scientist, my use of those terms (especially terms like 'porous' or 'under-fired', which are very common among tea-drinkers) would probably be very different to how others would understand the terms (and my use of such terms would probably be wrong most of the time).

I've been looking briefly at this: https://digitalfire.com/glossary/vitrification

That seems to suggest (to my untrained mind) that, within the field of ceramics, vitrification is not used to mean the stage at which something turns to glass (as it might mean elsewhere), but rather the process of how clays harden during firing.

But if anyone has other resources or explanations, then please feel free to share them.

(even so, I'm still at risk of calling my light-coloured LQER zini pot 'porous' and a bit 'under-fired', even if those terms are meaningless to a ceramicist...)

Andrew

[Baisao]

From what I read, it seems that you're saying that tea wax builds up inside the pot which is what is causing an effect, but I still don't think that is the case. If that was the case, new pots would all have either no effect or the same effect on tea which is not the case when you compare clays like zini and zhuni.

On the contrary: the fatty acids in teas accumulate and cover the interior surfaces of teapots to the detriment of the teas being brewed in them. They prevent the tea from interacting with the surface chemistry of the clay. It’s difficult to quantify but a little seasoning is helpful but it doesn’t take long for it to be detrimental. Diminishing returns, as it were.

So, contrary to the often stated idea that a lot of seasoning is good for tea and should be treasured, I believe that this seasoning can be bad for teas beyond a certain point. This is why I reset my pots after they begin to fall off. I recently reset half a dozen pots with decades of treasured seasoning because they were making mediocre tea. Tea is much better now from them. They’ll need to be reset in a year or two depending on how quickly they fall off.

No, the conversation about surface chemistry is that it is not pores that are making the difference but the dynamics between surface texture, chemicals in the clay, and chemicals in the tea. The chemical composition of a clay and the surface texture are fixed for a given teapot or cup, but do change how other chemicals react. This is happening on a very minute scale and is not something you’ll see even with a loupe.

You wouldn’t argue that glazed porcelain is unvitrified by any definition and yet some porcelains are muting and some reveal every flaw. They are, despite being pore-less and glasslike, capable of changing tea like Yixing teapots. Despite being smooth as glass, they have a varied enough surface texture— at the minute scale necessary— to make these changes to the chemistry of the tea.

@Andrew S, I agree with you regarding names and terms. It became apparent this morning that some of us have different understandings of the same terms and that all are right according to their context or discipline.

[Youzi]

Please link something that speaks to Yixing being vitrified.

Edit: Vitrification is the clay pretty much becoming glass. Yixing does not do this. Or am I completely off base?

Both of you are right. Yixing doesn't get vitrified. It gets sintered though. Which makes it impervious to water. In a high enough sintered state in which yixing is in. The clay particles are fused together, but There is still space between them, and the whole body is impervious to water.

You should imagine the impervious part of then inside of the teapot as a Mountain range with hills and valleys and some "caves" that don't run too deep.

Yixing is porous though. That can be easily measured and there's also a bunch of paper which measured the porosity of it. However it doesn't mean it's previous to water.

The process as I understand it is that clay moves from being 1) dry clay --> 2) sintered --> 3) bisque --> 4) earthenware --> 5) stoneware. The bisque fired pots I've handled were still pretty "raw" and that is more fired than sintered. The particles in a sintered matrix are barely fused, IIRC. This is why I say that Yixing is vitrified. The particles have melted together and fused in the matrix, though not as much as some stoneware that forms a glass matrix.

By sintering I didn't mean the state where water stops breaking down the clay body, but the type of fusion / process that happens throughout the firing stage, until the melting stage happens.

You can divide the firing into two phase, with the different states of densities you mentioned into:
The sintering phase -> the melting phase

So what I mean is that the particles are fused together by sintering and not by melting, like in porcelain.

After reading the tonnes of definition for vitrification and the state of being vitrified, maybe it's better to leave the whole term out of the way, as it's not relevant for yixing pots, and just leads to unnecessary confusion.

As you said yixing is stoneware which is impervious to water (doesn't weep), but it still has inner porosity of about 1-3%.

Yixing pots are usually fired till the end point of the sintering process before melting begins. That's 1100-1250 depending on the clay composition and the amount of Aluminum.

But imho the type of bonding between the particles doesn't really matter, for our discussions.

[wave_code]

On the contrary: the fatty acids in teas accumulate and cover the interior surfaces of teapots to the detriment of the teas being brewed in them. They prevent the tea from interacting with the surface chemistry of the clay. It’s difficult to quantify but a little seasoning is helpful but it doesn’t take long for it to be detrimental. Diminishing returns, as it were.

So, contrary to the often stated idea that a lot of seasoning is good for tea and should be treasured, I believe that this seasoning can be bad for teas beyond a certain point. This is why I reset my pots after they begin to fall off. I recently reset half a dozen pots with decades of treasured seasoning because they were making mediocre tea. Tea is much better now from them. They’ll need to be reset in a year or two depending on how quickly they fall off.

I recently reset a bunch of my pots as well as I found some of them were starting to really hurt a lot of the teas I was putting in them, or at least certainly not do them any favors. My idea is to "re-season" them, but in a different way. I had been thinking about this more and more, and what kept coming to mind was what you had said about your kettle seasoning and that it made ho hum water until one day it changed. Obviously some sort of surface chemistry and material science black magic going on there. But I kept thinking about it in terms of pots too, and how a lot of my early pots I probably "seasoned" to death in a bad way. Sure they get all nice and shiny, but I don't want gross build up on or in my pots, and they do seem to still get a nice surface shine albeit more slowly just from water alone being poured over them rather than really trying to raise them with washes of tea. I think sometimes when we use the term what some people mean is basically coating the inside of the pot by multiple sessions of letting tea stand in it for a long time... I'm trying to season them more by just their general use but also with thorough cleaning after each session, the exception being one longer soak to start for super absorbent/muting pots that really need a kick start to really be usable. I'm thinking more like minerals from the water building up very slowly and in certain places rather than building up a bunch of oils and residue in the pot. This is all in my head, but this much slower "seasoning" that is more a small gradual build up of minerals will have a more stable long term effect on my teas, and also not become gross. Sometimes the way certain people talk about seasoning and it sounds more like they are talking about a mistreated cast iron pan than a teapot.

[Youzi]

Letting you pot get dirty has no positive effects, neither does letting it scaled up. Btw, it's called tea scum in some circles or tea stain, a mix of leftover oils and calcium, if you want to look up some studies about it.

Also the shine on the outside should develop naturally, not from getting tea stain on the outside of the teapot. So it should be able to develop from dry brewing alone too. Actually that's a major sign of a teapot with well processed, good clay, fired correctly.

[Darbotek]

I bought this funky UFO pot from Yinchen (my love of oddly shaped wide pots knows no bounds). It brews wonderfully and it’s one of the most fun pots I have. Lots of pots work great and have the utilitarian features you need, but this pot is just fun to use. I’m curious about the surface imperfections though. They are matte when you angle the pot in the light.

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[Bok]

@Darbotek seems like unevenly blended clay of different colour.

[DailyTX]

Darbotek seems like unevenly blended clay of different colour.

@Bok do you think the uneven blend is intentional or accidental?