Twice-fired Yixing Pots?

[tingjunkie]

As it started to be discussed in the zhuni thread, I figured it should have its own topic. This is the first I'm hearing of Yixing being fired in a kiln twice, so I'm curious to know more about the process.

What are the benefits? What effect does it have on the pot's performance, if any? Is it done for cosmetic reasons, or performance reasons, or both? Can you tell a twice-fired pot by the look or feel? How rare or common is the process with modern pots?

Thanks!

[Alex]

I know very little on the subject of Yixing but I heard that refinements can be made to details in between firings. Be interested to hear what else it's used for though

[AT333]

As it started to be discussed in the zhuni thread, I figured it should have its own topic.

Just when i thought I was enjoying the festivities with all the contributions in that tread
This twice firing is something new to me too. Why they do that and if they can do it twice, can they do it more time? Is this the secret for desirable and rare multi color formation pot? Let the experts talk.

[kyarazen]

yes several firings can be done if required. i've taken notice that up to 4 firings can be done. if you participate in the taiwanese/chinese forums (even tieba etc), some of the artisans do show photos of their intermediate products, i.e. after first firing. they will spend time correcting the mouth of the pot and if the clay's good etc, not much problem, no need to sand the outer surface.

but if the clay's average, and flaws appear on the first firing, acid etching can be used to eat away molten iron spots, sanding and grinding can be done, and after that a thin layer of the same clay but in a very fine milled form is coated on for the 2nd firing. the surface will take on a "glowy" feel

its no big secret.. its just as a matter of fact as a statement that goes : the chinese eats noodles. electrical kilning has sped things up tremendously providing constant and fast temperatures, and convenience of firings.

the artisans would prefer to put their efforts to sell 1 pot that is seemingly well made, as opposed to the efforts to make and sell 10 shoddy shuiping pots.

[AT333]

Is repeated firing applicable only to newer pots? Any difference in new,CR,ROC etc era? Do they fire the pot and cover separately and calibrate both for perfect fitting? Most modern pots have perfect pot and cover fitting but CR pot tend to be poor fitting. Somehow around ROC period and earlier the cover and body fit is even better than CR pots. Do they calibrate by repeated firing too?

[kyarazen]

Is repeated firing applicable only to newer pots? Any difference in new,CR,ROC etc era? Do they fire the pot and cover separately and calibrate both for perfect fitting? Most modern pots have perfect pot and cover fitting but CR pot tend to be poor fitting. Somehow around ROC period and earlier the cover and body fit is even better than CR pots. Do they calibrate by repeated firing too?

not so much for ROC and earlier pots, but because they used dragon kilning for weeks for firing, the gradient of temperature increase and decrease is very gradual. this reduces things going out of shape. the down side of dragon kilning, it takes too much time, and the fire can be uneven, pots do come out quite ok looking, but they can be slightly under fired or over fired.

the only time when pots were re-fired in ROc and earlier is just to add glaze, like how wu yun gen had developed a 2 pass firing to make jun-yao yixings, and many more interiorly glazed items. but the difference with this is that the first pass firing has already gone at full temp, and the pot is fully fired, the 2nd pass on glaze is a lower temp firing just for the glaze. lead was added to the glaze to allow working with this reduced temperatures.

there's now criticism that only people attempting to "fake" old pots or factory pots would consider only one pass firing. but to what extent, i'm not sure. modern refiring, the first firing is done at lower temp, and then 2nd firing is at a higher temp.

[AT333]

Thanks kyarazen. Really appreciate your contribution. It helps to clear my clogged brain filled with teapot questions.

I am curious again.... Is the purpose of re-firing solely for the sake of fitting the teapot body and cover? For the ROC and earlier pots, the refiring purpose was to accommodate the glazing but how about the new ones? If it solely for fitting purpose, do they fire the cover and body attached together (and separate with another medium to prevent the cover and body sticking together? How about ROC pots, since the graduation of temperature has no effect on the fitting, is it a possibliity the body and cover is fired separately?

[kyarazen]

Thanks kyarazen. Really appreciate your contribution. It helps to clear my clogged brain filled with teapot questions.

I am curious again.... Is the purpose of re-firing solely for the sake of fitting the teapot body and cover? For the ROC and earlier pots, the refiring purpose was to accommodate the glazing but how about the new ones? If it solely for fitting purpose, do they fire the cover and body attached together (and separate with another medium to prevent the cover and body sticking together? How about ROC pots, since the graduation of temperature has no effect on the fitting, is it a possibliity the body and cover is fired separately?

re-firing can be to correct warp, surface problems, and always for the reason for fitting.

fired together! never separately. the reason why things go out of shape will probably be because of processing of clay quality, density, and the lid being smaller, looser, can shrink at a different rate/respond differently when subject to quick intense heat.

in principle yixing purple clay does not "fuse" to each other very significantly during firing since it doesnt "melt" except for occasional iron spotting that gets reduced from the overheating. but to prevent problems with lid sticking, either fine ground sillica powder (which is the appropriate material), or finely ground aluminum. for some reallly cheep and low quality yixings in the 80s, 90s, etc.. the aluminum shavings/powder remnants can be found in some of the pots! no goood

post firing, a wooden mallet is used to knock the lid loose, and hopefully does not crack/fracture anything

refer to following link for example on white sillica powder use between lid and body
http://blog.xuite.net/bolen0131/twblog/ ... 5%BF%3F%3F

[AT333]

Thank you very much kyarazen. Really appreciate it.

Many of those CR pots have loose cover fitting. Can we say they are just fit and fired only once?

Can we tell by looking at the texture or fitting of the pot (maybe with magnifying glass) the number of times the pot was fired?

Is there any effect on tea based on the number of times the pot is fired, assuming we compare two identical pot, one fired once and the other fired twice. I notice the beauty of variable temperature pots fired in dragon kiln perform differently for different tea. Does it works the same way with the number of times the pot is fired? I understand it is a too broad to answer type of questions perhaps just share with everyone so we can be in the lookout for answer or experience.

Thank you!

[kyarazen]

feels like a very public conversation we're having here

yes. in F1 from its inception till the 80s, they usually do single pass firing as they do not correct the pot

on the surface texture, it could be possible if they did coat a thin layer for refiring. it does take on a hard sheen with poor hydrophilicity. but if they dont re-coat and just refire only, the surface texture is probably quite similar to single pass. fitting wise, its still hard to say anything conclusive, many of my ROC to 60s pots have very good fits and they're single pass. perhaps its my luck because I usually get pots from collectors and these collectors might have already done some pre-screening during the days when these things were abundant. buying old pots off the shelf these days its hard to see perfect pieces, maybe impossible unless the price's right.

the debate on double or more pass fired yixings is that some chinese writers mention that the pot feels "lifeless". i have not spent sufficient time with modern pots to reach a conclusion.. ever since my start on yixing i had toyed with 80s stuff for a brief while before crawling into 70s and now into the earlier ones. I still think the pot shape and the wall thickness, the overall volume's contributes rather significantly to the pot's performance. the clay and the firing will determine catalytic properties, and that remains debatable.

on the other hand, I had positive experiences, especially on aromatics, on the usage of reduction fired pots. during dragon kiln days, many pots have "reduced cores" despite an overall red color, i had found these pots (the six/seven) that i have, interestingly able to benefit aromatics. another control experiment was to test two tokoname shudei pots, one was from yamada jozan, and the other was some peasantry ware, both from the earlier half of the 20th century, with dark/purplish black cores, these pots also significantly raise aromatics. as such, I would speculate that severely overfired clay may be too "oxidized" fired, and could be detrimental to tea. this is open for more experiments and more discussions if there are others whom are willing to spend the time to test.

the density and porosity is not simply the sieving. yixing clays have double porosity, the particles are porous like sponge balls. and as a clay on the whole the spaces between the particles are also pores. sieving determines the grind size, the finer the grind the lower the primary particle porosity. the secondary porosity of the pot will depend on how the clay is pounded, how microscopic air is pounded out, and also whether fluxing and glassification occurs.

Thank you very much kyarazen. Really appreciate it.

Many of those CR pots have loose cover fitting. Can we say they are just fit and fired only once?

Can we tell by looking at the texture or fitting of the pot (maybe with magnifying glass) the number of times the pot was fired?

Is there any effect on tea based on the number of times the pot is fired, assuming we compare two identical pot, one fired once and the other fired twice. I notice the beauty of variable temperature pots fired in dragon kiln perform differently for different tea. Does it works the same way with the number of times the pot is fired? I understand it is a too broad to answer type of questions perhaps just share with everyone so we can be in the lookout for answer or experience.

Thank you!

[.m.]

Thank you kyarazen for sharing with us.

How do you know that the core of some of your pots is reduced? Is it because you know that they come from a dragon kiln? Or because they are chipped?

And how does for example purion or shigaraki, which, from what i understand, go through repeated reduction/oxidation firing, fit your hypothesis? Do they have reduced core?

[AT333]

F1 from its inception till the 80s, they usually do single pass firing as they do not correct the pot

Thanks kyarazen. F1 pots generally seen to have better fit than F2 pots. But overall, F5 pots, although started in the late 70s and production on early 80s has the best fit. Could it be F5 started the repeated firing process. Could it be F1 better fit due to its firing process? If the gradual increase in temperature in the kiln produce better fit, probably F1 realised and practice it. But F2 group was also originated from F1 group and just curious why they did not follow the firing process? Could it be high demand during that time? F5 was in full force in the 80s producing large quantities round the clock and yet their fitting and workmanship is almost perfect.

[kyarazen]

Thank you kyarazen for sharing with us.

How do you know that the core of some of your pots is reduced? Is it because you know that they come from a dragon kiln? Or because they are chipped?

And how does for example purion or shigaraki, which, from what i understand, go through repeated reduction/oxidation firing, fit your hypothesis? Do they have reduced core?

for some, particularly the tokonames, they are chipped，revealing a dark core. for others, sometimes its possible to see hints/signs at areas of wear, i.e. edge of pot mouth where the lid goes past. there are also a couple of qing-roc pots that are hong ni but because of "yao-bian", it takes on a reddish black hue, its easy to tell the "reduction" on these.

i now tend to think of purion to be "neutral" ware and shigaraki to be mildly reduced. coming from an "aromatics" background, the effect of these clays is quite significant on the aromatics of some teas. oxidation fired yixings tend to dull down the aromatics of tea that have poor/weak aromatic traits.

[kyarazen]

F1 from its inception till the 80s, they usually do single pass firing as they do not correct the pot

Thanks kyarazen. F1 pots generally seen to have better fit than F2 pots. But overall, F5 pots, although started in the late 70s and production on early 80s has the best fit. Could it be F5 started the repeated firing process. Could it be F1 better fit due to its firing process? If the gradual increase in temperature in the kiln produce better fit, probably F1 realised and practice it. But F2 group was also originated from F1 group and just curious why they did not follow the firing process? Could it be high demand during that time? F5 was in full force in the 80s producing large quantities round the clock and yet their fitting and workmanship is almost perfect.

hmm.. i wouldnt dare to confidently compare F1 to F2 in terms of lid fit since the 60s to 70s were full of F1 pots with terrible fits F2 was set up to cope with added demand, so were other factories, and in a bid to increase production, less clay processing and aging, faster firing methods, etc, quality can be compromised. F1 always seemed to hold a "premium" over F2 all the time, and to date i've restructured almost all my collection to at least F1

i havent had many F5 pots, but for those i had, including an F5 zisha container i have.. the lid fits had always been very good. I would think the main reason was because F5 was primarily taiwanese funded, and being well funded and it was said that on some pots each artisan was only requested to make 1 pot a day to meet the exact specifications and qualities for the taiwanese market.

whether 2 pass was used by them i'm not sure, maybe i could ask a couple of authors/collectors that are working on the next yixing book on factory "花货"

[AT333]

Thanks kyarazen for your expertise