Yixing

[LeoFox]

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

Yes this was mentioned here:

viewtopic.php?p=6079#p6079


What bothers me about this one are the large error bars but I need to look at this paper more closely at some point. Thanks for the call out

[steanze]

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.

I disagree with this view. Pots with higher firing (and therefore greater sintering) are less porous and tend to have a more neutral effect on tea. Pots with high shrinkage (i.e. zhuni) also are less porous and tend to have a more neutral effect on tea. The claim that porosity has little to do with the effect of clay on tea is at the very least very controversial, and I don't know of strong empirical support for such a claim.

[LeoFox]

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.

I disagree with this view. Pots with higher firing (and therefore greater sintering) are less porous and tend to have a more neutral effect on tea. Pots with high shrinkage (i.e. zhuni) also are less porous and tend to have a more neutral effect on tea. The claim that porosity has little to do with the effect of clay on tea is at the very least very controversial, and I don't know of strong empirical support for such a claim.

I started looking into porosity under the assumption that porosity scales with rounding. However, I've found at least with my limited sampling of pots, this is not the case and impact on tea is potentially a much more complex issue than just porosity. I wish I had more pots to play with but unlike some on here, I am limited by how much I can spend both in terms of money and time.

[steanze]

I started looking into porosity under the assumption that porosity scales with rounding. However, I've found at least with my limited sampling of pots, this is not the case and impact on tea is potentially a much more complex issue than just porosity. I wish I had more pots to play with but unlike some on here, I am limited by how much I can spend both in terms of money and time.

I looked at the analyses you did, and the tests you ran are very cool. It's great that you took the time to collect those measurements. I also agree with you that "porosity" defined as % of empty space is in many ways too simplistic, and that for instance void space accessible from the surface is probably more relevant. The structure of this space is likely to also play a role (i.e. two pots might both have 1% increase in weight when wet, but the average size of void spaces may be different between the two: one might have many small cavities, the other might have fewer larger ones).

Regarding your measurements, I am a bit concerned about the strategy of weighting pots once they are "visually dry". It seems hard to use this as a reliable objective criterion. Is it possible that some clays look "visually dry" after different amounts of drying, because of the clay's composition? Is it possible that letting the pot become visually dry on its own vs patting it dry with a cloth would lead to different amounts of water removal? I worry that these sort of things might make it hard to find a relationship between porosity and effect on tea, because of noise injected by the variation in terms of when a pot is deemed to be "visually dry". Maybe one way to test this would be to take multiple measurements for the same pot, and evaluating how replicable the measurements for one pot are. I still think it's great that you are working on taking precise measurements, that's a step in the right direction and one that not many of the rest of us had bothered to do, so thanks for helping to push the understanding of the effects of clay on tea further!

[LeoFox]

I started looking into porosity under the assumption that porosity scales with rounding. However, I've found at least with my limited sampling of pots, this is not the case and impact on tea is potentially a much more complex issue than just porosity. I wish I had more pots to play with but unlike some on here, I am limited by how much I can spend both in terms of money and time.

I looked at the analyses you did, and the tests you ran are very cool. It's great that you took the time to collect those measurements. I also agree with you that "porosity" defined as % of empty space is in many ways too simplistic, and that for instance void space accessible from the surface is probably more relevant. The structure of this space is likely to also play a role (i.e. two pots might both have 1% increase in weight when wet, but the average size of void spaces may be different between the two: one might have many small cavities, the other might have fewer larger ones).

Regarding your measurements, I am a bit concerned about the strategy of weighting pots once they are "visually dry". It seems hard to use this as a reliable objective criterion. Is it possible that some clays look "visually dry" after different amounts of drying, because of the clay's composition? Is it possible that letting the pot become visually dry on its own vs patting it dry with a cloth would lead to different amounts of water removal? I worry that these sort of things might make it hard to find a relationship between porosity and effect on tea, because of noise injected by the variation in terms of when a pot is deemed to be "visually dry". Maybe one way to test this would be to take multiple measurements for the same pot, and evaluating how replicable the measurements for one pot are. I still think it's great that you are working on taking precise measurements, that's a step in the right direction and one that not many of the rest of us had bothered to do, so thanks for helping to push the understanding of the effects of clay on tea further!

Thanks for your kind comments!

Yeah this drying issue worried me too- and that is why I did repeat it a few times but did not show the results here. They have a 0.1% change in mass error. That is why I decided to delete all my results for those pots that showed less than 0.1% change in mass, which works about to about 0.06-0.09g for my different pots.

The structure of this space is likely to also play a role (i.e. two pots might both have 1% increase in weight when wet, but the average size of void spaces may be different between the two: one might have many small cavities, the other might have fewer larger ones).

This is a very good point and I am not sure how to address this other than place it in the discussion as we often do to satisfy the reviewers

What I am really shocked about is how long it takes a very porous pot to dry. That hqsn literally takes more than 40 hours to dry while a similar sized pot takes less than 5 minutes.

I really am tempted to hunt for more super porous pots but my budget...

Perhaps the ideal would be if several pots can be made with same shape and similar volume and same clay but with different firing procedures to achieve a range of porosities - and then tested side by side multiple times with one tea and by a group of experienced tea drinkers that have shown a degree of alignment. But who can and would be willing to do this other than a teapot/tea company? And if so, who can trust their report since they have a profit motive?

[olivierd]

I started looking into porosity under the assumption that porosity scales with rounding. However, I've found at least with my limited sampling of pots, this is not the case and impact on tea is potentially a much more complex issue than just porosity. I wish I had more pots to play with but unlike some on here, I am limited by how much I can spend both in terms of money and time.

Porosity increases the contact surface. Without hard data, I would tend to believe that the total effect (or chemical reaction) is a mix of clay composition AND porosity. Steanze is likely right : higher fired, less porous pots would yield less effect for the same clay. You need two pots from the same period and clay with different firings

[LeoFox]

I started looking into porosity under the assumption that porosity scales with rounding. However, I've found at least with my limited sampling of pots, this is not the case and impact on tea is potentially a much more complex issue than just porosity. I wish I had more pots to play with but unlike some on here, I am limited by how much I can spend both in terms of money and time.

Porosity increases the contact surface. Without hard data, I would tend to believe that the total effect (or chemical reaction) is a mix of clay composition AND porosity. Steanze is likely right : higher fired, less porous pots would yield less effect for the same clay. You need two pots from the same period and clay with different firings

I think porosity is one quality attribute that is linked to accessible surface area. Another is texture, which can have a significant contribution.

Your post highlights something important to me. While it may be true that all else being equal, accessible surface area will make an impact. But how likely are we going to find and buy pots with "all else equal"?

As a pot buyer, I am usually getting some pot with unknown firing and clay composition. The vendor makes some claims but how accurate are they? With this in mind, can I say that this pot must be rounding if it is porous or this pot must be neutral because it is not porous? I cannot because I do not have enough information on the composition or firing process.

Case in point is the kobiwako clay that is very popular on here. It has practically no porosity but it has a rough texture. It definitely mutes the scent and some of the aroma to the point it completely shifts the experience when drinking gao shan. Since it cannot be porosity, then it might have something to with composition and texture. But if I were to make the assumption that this pot cannot be rounding because it is not porous, then I would make a mistake. In fact, I would be making many mistakes about most of my pots

[steanze]

Yeah this drying issue worried me too- and that is why I did repeat it a few times but did not show the results here. They have a 0.1% change in mass error. That is why I decided to delete all my results for those pots that showed less than 0.1% change in mass, which works about to about 0.06-0.09g for my different pots.

Ah, very good, this is helpful!

The structure of this space is likely to also play a role (i.e. two pots might both have 1% increase in weight when wet, but the average size of void spaces may be different between the two: one might have many small cavities, the other might have fewer larger ones).

This is a very good point and I am not sure how to address this other than place it in the discussion as we often do to satisfy the reviewers

Yes, I also would not know how to address this. In my experience, teapots with clay ground to a finer mesh tend to have a more neutral effect on tea as compared to teapots ground to a coarser mesh, even when they are made of similar ore. This makes me suspect that the size of the void spaces might be important, but I cannot be confident based on this observation alone, because coarser clay might also lead to less overall sintering, so particle size might correlate with both the size of void spaces and with the change in mass when wet, making it hard to decorrelate the two.

Perhaps the ideal would be if several pots can be made with same shape and similar volume and same clay but with different firing procedures to achieve a range of porosities - and then tested side by side multiple times with one tea and by a group of experienced tea drinkers that have shown a degree of alignment. But who can and would be willing to do this other than a teapot/tea company? And if so, who can trust their report since they have a profit motive?

I am trying to make this happen...

[LeoFox]

I am trying to make this happen...

[steanze]

Case in point is the kobiwako clay that is very popular on here. It has practically no porosity but it has a rough texture. It definitely mutes the scent and some of the aroma to the point it completely shifts the experience when drinking gao shan. Since it cannot be porosity, then it might have something to with composition and texture. But if I were to make the assumption that this pot cannot be rounding because it is not porous, then I would make a mistake. In fact, I would be making many mistakes about most of my pots

Interesting thoughts. Are we sure that the kobiwako has no porosity? Could it have pores such that the water goes in but also out easily, so that it does not have much increase in weight when it is visually dry?

[LeoFox]

Case in point is the kobiwako clay that is very popular on here. It has practically no porosity but it has a rough texture. It definitely mutes the scent and some of the aroma to the point it completely shifts the experience when drinking gao shan. Since it cannot be porosity, then it might have something to with composition and texture. But if I were to make the assumption that this pot cannot be rounding because it is not porous, then I would make a mistake. In fact, I would be making many mistakes about most of my pots

Interesting thoughts. Are we sure that the kobiwako has no porosity? Could it have pores such that the water goes in but also out easily, so that it does not have much increase in weight when it is visually dry?

I guess that could be "texture" - that is deviation of actual surface from ideal averaged surface. I understand this is an important quality attribute for mechanical industrial items where the potential for friction must be tightly controlled. I think this is commonly measured using microscopy. In some ways, I wonder If youzi's method accounts for this: measuring the wet surface. On the other hand, youzi's method may simply be accounting for surface tension effects across uneven surface. In any case, I will use his method for a few pots but not kobi because I'm using it 2x a day right now.


Actually, Victoria used a method that Is closer to youzi's method. I think her finding is also minimal change for kobi

viewtopic.php?p=37076#p37076

[steanze]

Good things to think about...
I read the linked post, but I am not sure I understand why that would account for the possibility that a pot might have pores in which water goes easily in and out.

I guess at this point I have a few questions I am wondering about (these are things for all of us to try to figure out together). The first one is whether it's easier to absorb water from larger pores than from smaller pores when patting dry with a cloth. The fibers of the cloth might enter the larger pores but not the smaller pores. Like this (excuse the poor drawing):

pattingdry.jpg (31.4 KiB) Viewed 5791 times

This might account for the surprising results that some pots that we expected to be porous (like the Tachi Masaki) were associated with fairly low weight gain.

When people talk about how "porous" a teapot is in the context of Yixing , I tend to interpret this to include all kinds of clay structure properties that affect the tea, and to not include properties that do not affect the tea (i.e. a pot that has very very tiny pores that do not affect the tea would not be "porous" for tea-making purposes). The idea that the effect of Yixing depends on "porosity" (in this loose sense) is in contrast to accounts for which the effect of Yixing teapots results from chemicals in the teapot that leach into the tea.

If we want to understand more precisely what kinds of clay structure properties affect tea, I suspect that we need to ask some hard questions, for example - "what is a pore?" To take a few cases, which ones of these are pores?

pores.jpg (52.19 KiB) Viewed 5791 times

It feels like we have to draw an arbitrary line. We don't want to get stuck with an issue of terminology. Perhaps for the time being it is useful to think that there might be some properties of clay structure that affect the tea. I am not going to call these properties "pores", because I am not sure how to define a pore precisely enough. What would be interesting to know, then, is what these properties have to be like (i.e. shape and size of cavities/texture irregularities) in order to affect the tea. Then, it would be interesting to know what these properties have to be like (i.e. shape and size of cavities/texture irregularities) in order to trap water. And finally, it would be interesting to know whether and to what extent cavities/texture irregularities that affect the tea also trap water, and vice versa. It is plausible that there will be some properties of clay structure that will affect tea, and some others that will not. For example, we might find some pots that have very very tiny cavities/texture irregularities, and those are too small to affect the tea. Maybe they will still be large enough to trap water. We might also find pots with cavities/texture irregularities that are too large to trap water (i.e. if water goes in but also comes out easily), but that do affect the tea. I suspect that understanding this will require some microscopy.

It is not immediately obvious whether in general we should reserve the name "pores" for the cavities/texture irregularities that trap water, or whether we should reserve it for the cavities/texture irregularities that affect the tea. Finding that a pot that does not trap much water still affects the tea might be evidence that something other than clay structure affects the tea, but it might alternatively be evidence that there are properties of clay structure that affect the tea but do not trap water.

Finally, it is also possible that the effect on tea does not depend on clay structure/cavities/texture, or that it depends jointly on clay structure and something else. So far, however, I have not seen very compelling hypotheses for what that something else would be...

[.m.]

When people talk about how "porous" a teapot is in the context of Yixing , I tend to interpret this to include all kinds of clay structure properties that affect the tea, and to not include properties that do not affect the tea (i.e. a pot that has very very tiny pores that do not affect the tea would not be "porous" for tea-making purposes). The idea that the effect of Yixing depends on "porosity" (in this loose sense) is in contrast to accounts for which the effect of Yixing teapots results from chemicals in the teapot that leach into the tea.

I tend to think about a third option where the tea catalytically reacts at the contact with the teapot surface but the chemical/material structure of the pot is largely unchanged. If this is the case then what matters is both the reactivity and the relative area of the surface on which this happens. The contact area depends on the "jaggedness" of the surface, on its fractal properties. This is certainly related to porosity, but different, since porosity is usually defined as the ratio of volume of cavities, not as their area.

[LeoFox]

When people talk about how "porous" a teapot is in the context of Yixing , I tend to interpret this to include all kinds of clay structure properties that affect the tea, and to not include properties that do not affect the tea (i.e. a pot that has very very tiny pores that do not affect the tea would not be "porous" for tea-making purposes). The idea that the effect of Yixing depends on "porosity" (in this loose sense) is in contrast to accounts for which the effect of Yixing teapots results from chemicals in the teapot that leach into the tea.

I tend to think about a third option where the tea catalytically reacts at the contact with the teapot surface but the chemical/material structure of the pot is largely unchanged. If this is the case then what matters is both the reactivity and the relative area of the surface on which this happens. The contact area depends on the "jaggedness" of the surface, on its fractal properties. This is certainly related to porosity, but different, since porosity is usually defined as the ratio of volume of cavities, not as their area.

https://www.sciencedirect.com/science/a ... 6384900424

[.m.]

When people talk about how "porous" a teapot is in the context of Yixing , I tend to interpret this to include all kinds of clay structure properties that affect the tea, and to not include properties that do not affect the tea (i.e. a pot that has very very tiny pores that do not affect the tea would not be "porous" for tea-making purposes). The idea that the effect of Yixing depends on "porosity" (in this loose sense) is in contrast to accounts for which the effect of Yixing teapots results from chemicals in the teapot that leach into the tea.

I tend to think about a third option where the tea catalytically reacts at the contact with the teapot surface but the chemical/material structure of the pot is largely unchanged. If this is the case then what matters is both the reactivity and the relative area of the surface on which this happens. The contact area depends on the "jaggedness" of the surface, on its fractal properties. This is certainly related to porosity, but different, since porosity is usually defined as the ratio of volume of cavities, not as their area.

https://www.sciencedirect.com/science/a ... 6384900424

Yes!
But of course, in the absence of a high resolution microscope, measuring the weight of dry vs wet teapot is probably still the best tool to get at least some partial information.