Firing/Density


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Firing/Density

Postby wert » Nov 3rd, '13, 03:42

I often read about a teapot being high-fired or low-fired, how would it affect the brew? How can I know the firing of my teapots? Also clay density is also sometimes indicted, and hence the same questions, how does it affect the brew and how do I check?

I know nothing about any of these stuff even I had been drinking tea all along and using zisha teapot for sometime. Ignorance is bliss?
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Re: Firing/Density

Postby togei » Nov 3rd, '13, 17:42

A simple start might be that a high fired body won't absorb or wick any liquids, a low fire body will.
How that affects tea taste maybe someone else can answer.
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Re: Firing/Density

Postby tingjunkie » Nov 3rd, '13, 19:01

Speaking in broad generalities of course...

The higher the firing or higher the density, the more the pot will behave similarly to porcelain. It will keep the higher notes and subtle nuances of flavor and aroma, but the mouthfeel may be thinner or sharper.

The lower the firing or the density, the more the pot will absorb and round off subtle flavors and aromas, but the mouthfeel with be thickened or made smoother. The exception to this is if the pot is underfired (i.e. fired even below the acceptable range so it has a clay smell to it still) then it will make tea that gives an unpleasant prickly/choking sensation in the throat.

Now, if we throw in the wall thickness and heat retention, or even the clay's mineral/metal composition and quality, then we add even more variables that will influence how the tea comes out. So, it's even possible a lower fired pot with great clay will protect more of the flavors and aromas than a higher fired pot made with bad clay.

So... take it as a guideline, rather than a rule. :wink:

As for how to tell if your pot is higher or lower fired, it's really just a comparison thing. You need to handle and compare a lot of pots. The things to look for are the sound the pot makes when the lid is dropped in place from a couple mm high (higher fired and denser will give a higher pitch), and the feel of the pot on your hands (higher fired and denser will be smoother to the touch, ignoring pots which have sand added for the look of course).
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Re: Firing/Density

Postby JBaymore » Nov 3rd, '13, 23:17

The firing temperature is no guarantee of the fired clay's porisity. In this discussion density and porosity seem to the used somewhat as synonyms.

If you look at Hagi, for an example, it is fired at a relatively high temperature, but is still a bit porous. This quality of certain clays is known as refractoriness. Fireclays withstand very high temperatures with out beginning to virtify (form a significant glassy phase). Ditto pure kaolins. Same with many ball clays.

On the other side of the coin, many lower fired clays can have such a content of materials that flux the silica content, that they tend to develop larger amounts of glassy phase materials... and hence become less porous.

This is a highly complex technical subject.

best,

..............john
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Re: Firing/Density

Postby tingjunkie » Nov 3rd, '13, 23:27

Of course, John is correct. If we are talking Yixing pots, zhuni clay is fired at lower temps than other clays, yet it is often considered very "high fired" due to its high density and low porosity.

I guess there are bastardized tea drinker terms, and correct ceramic artist terms. :D
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Re: Firing/Density

Postby Tead Off » Nov 4th, '13, 00:11

wert wrote:I often read about a teapot being high-fired or low-fired, how would it affect the brew? How can I know the firing of my teapots? Also clay density is also sometimes indicted, and hence the same questions, how does it affect the brew and how do I check?

I know nothing about any of these stuff even I had been drinking tea all along and using zisha teapot for sometime. Ignorance is bliss?

As you can see, there is no one size fits all description of clays, and their subsequent processing and firing by the potter. Each clay has its own characteristics and mineral composition that determine how it gets fired and how it will relate to tea brewing. On top of that, type of kiln, firing techniques, and a host of other variables determine the final product. Can two potters take the same clay and get identical results?

If you are buying directly from a potter or rep of that potter, you will be able to find out all necessary information about clay and firing. If you are buying in a general market place, this will be difficult to find out precise information about clay and firing. In either case, you will be left to your own devices in determining what teapots and tea go best together. Every tea drinker goes through their own process of determination to find the best match. That's the fun of this subject. And, it takes plenty of money to play this game. :D
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Re: Firing/Density

Postby chrl42 » Nov 4th, '13, 01:01

JBaymore wrote:The firing temperature is no guarantee of the fired clay's porisity. In this discussion density and porosity seem to the used somewhat as synonyms.

If you look at Hagi, for an example, it is fired at a relatively high temperature, but is still a bit porous. This quality of certain clays is known as refractoriness. Fireclays withstand very high temperatures with out beginning to virtify (form a significant glassy phase). Ditto pure kaolins. Same with many ball clays.

On the other side of the coin, many lower fired clays can have such a content of materials that flux the silica content, that they tend to develop larger amounts of glassy phase materials... and hence become less porous.

This is a highly complex technical subject.

best,

..............john

Yixing potters tends to classify Yixing clay as 'clay or mud(泥)' and 'sand(砂)'.

Techinically speaking, sand types are said to lack the plasticity (like Di Cao Qing or Duanni)..so potters store the clay for long or mix with other clays in order to enhance the plasticity. Sand types basically have high temperature to fire (point of crystallization)..IMO sand types are closer to stone whereas clay types are close to mud.

Zhuni clay is said to be a pure mud type..good to handle yet easily gets warped or shrink, they said this clay doesn't have 'bone (sand)'.

IMHO half sand/half clay types 泥砂質 are idle to brew tea..in fact many high-quality Yixing clays are of this kind of mixture....but anyway high-quality Yixing clays are super-rare these days.
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Re: Firing/Density

Postby wert » Nov 4th, '13, 02:02

In this case, when a vendor labels a teapot in terms such as high-fired or high density, it is almost nearly useless information in regards to how it would be perform? As noted by others, there are many other factors such as kiln/mineral content etc.
Tead Off wrote:If you are buying directly from a potter or rep of that potter, you will be able to find out all necessary information about clay and firing. If you are buying in a general market place, this will be difficult to find out precise information about clay and firing. In either case, you will be left to your own devices in determining what teapots and tea go best together. Every tea drinker goes through their own process of determination to find the best match. That's the fun of this subject. And, it takes plenty of money to play this game. :D
I do have something of a happy problem, I already had more than a few zisha pots. I had not bought any new pots for like 10 years + till recently when I bought a couple off the forum.

When I bought the pots then (and now) I had no clue on the potter or type of clay used and other factors, I just bought them on aesthetics and touch. So, I had been happily using these 5-6 pots regularly without a clue how to use them "scientifically". I don't even use them for any individually tea (although, I only drink a few types regularly).Mostly, I just used them according to my mood. Over time, I do tend to use certain tea with certain pots. I guess there is no real "correct" way of using them, just the general guidelines.

In additional to what I am using, that there is number of pots lying around the house, either gifts or bought by family members years ago. I am curious to find out more of their background. How can I go about it? Any teapot masters I can ask for help? I am quite sure they are not valuable as they are commercial pots of no great age but treasure is treasure. :)
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Re: Firing/Density

Postby Tead Off » Nov 4th, '13, 03:02

wert wrote:In additional to what I am using, that there is number of pots lying around the house, either gifts or bought by family members years ago. I am curious to find out more of their background. How can I go about it? Any teapot masters I can ask for help? I am quite sure they are not valuable as they are commercial pots of no great age but treasure is treasure. :)

If you are talking about Yixing teapots, you can post here and ask questions about your pots to find out any further info. Chops that identify the artist can help to find info on clay and how the potter worked. That is, if you can find someone who knows/knew him/her. Sometimes it is easy to identify a clay from the photo but color can vary according to your camera/computer settings.

One of the many things people do is test the sound of their teapots for the type of 'ring' it gives them. With thin, bone porcelain, you will get an almost metallic ring. These are high fired, but there are other clays giving high rings that are not fired as high as porcelain, and high fired clays that don't have high 'rings'. Confusing, huh? Thickness of clay will affect the ring.

The one factor for me that I often observe that affects tea the most is the iron content in the clay. Even in unrefined porcelain, the additional iron affects the tea. How this works with each tea is probably not the same and each teapot will have a different relationship with different teas. Will the same teapot brew great Wuyi tea and Darjeelings? These two teas are very different yet I have pots(same ones) that will brew both of these very well. It is science yet not science. I continue to observe but I have not come to any scientific conclusions. :D
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Re: Firing/Density

Postby wyardley » Nov 4th, '13, 03:04

wert wrote:When I bought the pots then (and now) I had no clue on the potter or type of clay used and other factors, I just bought them on aesthetics and touch. So, I had been happily using these 5-6 pots regularly without a clue how to use them "scientifically". I don't even use them for any individually tea (although, I only drink a few types regularly).Mostly, I just used them according to my mood. Over time, I do tend to use certain tea with certain pots. I guess there is no real "correct" way of using them, just the general guidelines.

I think your approach is fine (and I suspect you already know that). Personally, I'm not a potter, and don't really care to try and guess what temperature a pot was fired at, or even spend my time thinking about it. Using your senses / intuition to match a pot to tea is a perfectly appropriate way to do it.

But in a general sense, I think appearance, weight, sound, and feel probably give some clues, as does the way tea oils are absorbed. Certain pots just seem to "absorb" a lot of everything (duller, more porous appearance, duller sound, smooth out the taste of tea more), and others seem to reflect more.
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Re: Firing/Density

Postby wert » Nov 4th, '13, 21:34

Tead Off wrote:One of the many things people do is test the sound of their teapots for the type of 'ring' it gives them. With thin, bone porcelain, you will get an almost metallic ring. These are high fired, but there are other clays giving high rings that are not fired as high as porcelain, and high fired clays that don't have high 'rings'. Confusing, huh? Thickness of clay will affect the ring.
This is something that bothers me a bit on how some "dark clay" that ring higher pitch than those red ones. It makes sense thickness plays a big role on the ring. Everything is connected to everything else and everything is a general guideline. Red = higher iron content? generally, I suppose.
wyardley wrote:I think your approach is fine (and I suspect you already know that). Personally, I'm not a potter, and don't really care to try and guess what temperature a pot was fired at, or even spend my time thinking about it. Using your senses / intuition to match a pot to tea is a perfectly appropriate way to do it.
Well, I don't know any other approach, hoping to find one but I guess there is really none. The more I tried to find out, the more confused I am. :D

I would try to take some decent photos of my pots and ask for more advice then.
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Re: Firing/Density

Postby Chip » Nov 5th, '13, 11:39

Some potters will tell you what the firing temp and duration was (sometimes right in the product description) ... this is mostly more Western potters where communication is more practical.
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Re: Firing/Density

Postby paul haigh » Nov 5th, '13, 16:29

The funkier I get, the less dense my pieces are, and my work is fired to very high heat (like well over cone 13 in the middle of the kiln). Some of the wilder clays have lots of organics that burn out, making them less dense when fired.
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Re: Firing/Density

Postby Chip » Nov 5th, '13, 16:36

paul haigh wrote:The funkier I get, the less dense my pieces are, and my work is fired to very high heat (like well over cone 13 in the middle of the kiln). Some of the wilder clays have lots of organics that burn out, making them less dense when fired.

Paul, perhaps it would be helpful to readers if you would share what cone 13 or any cone designation means?

Thanks!
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Re: Firing/Density

Postby JBaymore » Nov 5th, '13, 16:55

Chip wrote:
paul haigh wrote:The funkier I get, the less dense my pieces are, and my work is fired to very high heat (like well over cone 13 in the middle of the kiln). Some of the wilder clays have lots of organics that burn out, making them less dense when fired.

Paul, perhaps it would be helpful to readers if you would share what cone 13 or any cone designation means?

Thanks!


Aha,.... now you are grilling a fomer student........ I get to see him in the "hot seat". heh...heh....heh. :evil: :lol: :wink:

best,

.............john
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