Wood fired porcelain

[betta]

Wood fired Japanese teaware is quite often seen, but have anyone heard of wood fired chinese porcelain? what's so special with it and how can we identify if the piece is wood fired or not?
Any comment is appreciated.

[Chip]

You could ask the TA's in the Ask the Artisan topic ... under TeawareArtisans forum of TC.

My very limited experience is that they often have a Yohen (changed by the fire) look to the Japanese ones (usually clay, not porcelain). I will usually mentally say wood fired, then read the description.

But this is from very limited experience.

I don't know if I ever saw Chinese wares described as wood fired, or maybe I just never noticed.

[bearsbearsbears]

Most older Chinese wares would be wood fired, and certainly all antique stuff. Some porcelains change color (they're said to "blush") in gas and wood reduction environments, but glaze stops this clay-and-fire reaction.

Japanese and American potters who wood fire porcelain do so for the "yohen", as Chip indicates.

As far as porcelain covered in a clear glaze--qinghua, for example--potters want to minimize the effect of the fire as much as possible, so it's not likely that a visible difference is noticeable unless viewing two pieces in the same glaze at the same temperature where one was fired gas and one wood. Even then, whether the glaze is clearer or the clay whiter in one firing or another has as much to do with the clay and glaze recipes as the firing fuel.

Wood firing is very important to the depth of color in Chinese celadons; in fact, one kiln producing superior imperial celadon added green pine wood with needles attached toward the end of the firing to achieve a particularly awesome depth of color, as I recall reading at the Taiwan National Gallery (I think).

[TomVerlain]

there is no one answer, as the type of glaze reacts differently under temperture flucuations, time to heat up, cool down, top temperture, etc. The ideal of wood would be the controlability of gas.

I belive a simple indicator is eveness of bubbles in the glaze. Gas fired is much more uniform.

User grade 19th c and early pieces might have ash or other fairly large artifacts in the glaze from the uneven firing process.

Forgers who truly want to fool would use wood fired to counterfiet pieces, cheap imitations would be gas fired and shaped more niavely to appear older. Artistic peice might be wood fired for the asthetic. I really do not think you will find too much mass produced porcelain wood fired, unless you are paying for the previlege.

[betta]

Chip, Bears, thanks for sharing this info. It's a deep insight on the firing/fuel process. Before this, I thought that that the wood firing was used in the past because wood was the main fuel available at that time. Nice to know that they have significant influence to the color of the piece.

Tom has hit the bull's eye about the reason I raised this topic: vintage porcelain. I've never thought of distinguishing wood fired from the gas fired porcelain teaware before, so I don't know exactly what to see in this case. Thank you.

[JBaymore]

Prior to a certain point in time, ALL porcelain was wood fired. It was the fuel available. If the "mark of the fire" was not wanted... it was a problem to be overcome.

One of the prime qualities that porcelain became prized for was its whiteness and "purity".

As was mentioned above, often the cheap wares for the masses were open stacked so that lots of pieces could fit into a specific area of the kiln. But the real "good" work was fired in something called "saggars". Saggars are kiln furniture that you can think of as "covered jars". The pot to be fired was places inside a bigger pot, and then anopther on of those "pot and saggar" combinations was places vertically on top of the one below. And so on in "bungs" of pots and saggars.

In fact, at one time the formulation and production of porcelain was a highly guarded and valuable secret. Like the schematics for the latest Intel chip. What you might call "industrial espionage" was the way that the secret got out of China .

best,

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

[chicagopotter]

As was mentioned above, often the cheap wares for the masses were open stacked so that lots of pieces could fit into a specific area of the kiln. But the real "good" work was fired in something called "saggars". Saggars are kiln furniture that you can think of as "covered jars". The pot to be fired was places inside a bigger pot, and then anopther on of those "pot and saggar" combinations was places vertically on top of the one below. And so on in "bungs" of pots and saggars.

Here are a couple of links to porcelain items fused into saggars: http://www.trocadero.com/brianpage/item ... store.html and http://www.trocadero.com/brianpage/item ... store.html.

[betta]

Thanks, John and Chicagopotter.

I wonder at the same firing batch, how does the finished porcelain in saggar look like compare to those stacked inside the kiln?
Is there any distinct characteristic visible to naked eye?

[JBaymore]

I wonder at the same firing batch, how does the finished porcelain in saggar look like compare to those stacked inside the kiln?
Is there any distinct characteristic visible to naked eye?

One of the characteristics of wood firing is the tendency for volatile compounds like sodium oxide and potassium ocxide in the wood ash to vaporize and create markings on the wares. Another is the fact that some light wood ash itself is carried from the fire boxes with the draft of the circulating gases through the kiln on the way to the exit flues and settles onto the wares. The vaporization effects are usually refered to as "flashing" (in English) and the ash deposits are called "natural ash glaze".

Both of these effects can be either a benefit or a defect.... depending on the aesthetic effect you are trying to produce . For porcelain....... usually looked at as a defect; lessening the "purity".

Early potters seeing this this melting wood ash accumulating on certain areas of the pots is the genesis for the development of applied high fired glazes.

So on porcelains that are fired in the "open stack", there is great likelihood that you will see some flashing markings of some sort, and also some speckling of the typically "darker than white" wood ash. Flashing on bare porcelain will usually show a peachy to salmon blush. melting wood ash can typically be anywhere from grey to icy greens and blues (a bit like celadons).

Wood ash and flashing vapors hitting onto glazed areas of porcelain takes on completely different characteristics, as the chemistry reacts with the underlying glaze chemistry. Hard to characterize simply. On white glazes the speckling of wood ash could just be darker speckles. On black tenmoku glazes it could be lighter speckles. On a chun or copper red... it could result in an area of distinctly different color. Can't say completely without posting tons of pictures and writing a book .

Hope this helps.

best,

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

[togei]

I have fired glazed porcelain both inside a saggar type thing and in the rough. It is very easy to tell with either white, i.e., clear glazed porcelain, or something more along the celedon side if a saggar was used or not. Fired in the rough, that is, with out some kind of protection, will have specks of color in areas towards the flow of fire; the areas that are closer to the firebox, away from the exit flues. These specks, in my work, range from brown to black. The black is probably fly something, not ash. That is to say something that is caught up in the flow of the hot air that is robust enough not to melt at 1,100-1,250 C. There will also be, on each individual piece, a 'himae' and 'hioku'. 'Himae' is the area closer to the fire, 'hioku' is the area closer to the chimney. This distinction will sometimes be very obvious, sometimes not. The himae/hioku distinction may be a deeper color on the himae side, it might be the glaze is less melted on the hioku side or some other indication. In the case of my kiln one of the himae/hioku indicators,90% of the time, is teabowl type footed ware has a distinct and noticeable tilt toward himae, toward the fire. Himae/hioku should be discernible on all wood fired work that wasn't fired in a saggar. Fired in a saggar won't have great himae/hioku if there is a good seal. I should say I don't use proper saggars. I always fire in the rough, without saggars.
The pitting that John wrote about is visible in all my glazed work fired in the open. I haven't done a lot of thinking about it so can't say with certainty anything about it. It seems to be from either fly ash that settles at high temperatures on a semi-molten glaze, leaving an impression but no ash since the physical ash burns out or caused by atmospherics in the kiln. I only fire wood fueled kilns so haven't done any detailed examination but I believe the pressure in a wood fueled kiln greatly affects the final look/feel.
Regarding bubbles in the glaze.
I have some Edo period celedon bowls out in my showroom. I have looked at the glaze through a magnifying glass because I too have some questions regarding bubble distribution. I think the type of bubbles and pitting are two indicators of authenticity. Even if these two characteristics are present it is possible the piece isn't authentic if authentic = from a certain period in the past.
Regarding wood as a fuel.
If my memory serves, there was a big division in China regarding use of wood and coal from the Song period on, maybe earlier. All areas initially used wood but one rather quickly turned to coal. Someone with more expertise please correct me.
There is an excellent lecture series available on Itunes U on Chinese porcelain and the Silk road. The names of the 3 series are Passport to Asia, Gods and goods, and By Land and By Sea with the "By" in the last title being a symbol that means 'by'.
I say the lecture series is excellent which it is. Not all of the lecturers are excellent though.

[betta]

John, thanks once again for the info.

Togei, I enjoyed reading your straightforward but detailed explanation. It answered all of my questions. Thank you.

[JBaymore]

Here's a visual example of the interior of an "open stacked" porcelain bowl piece fired in the back part of a noborigama wood fired kiln (a good way away from both the main and the chamber firebox... so not getting huge amounts of "fly ash" and "fly ?")............

BruceWoodPorcelainBowlDetail1-jcb.jpg (22.59 KiB) Viewed 2343 times

BruceWoodPorcelainBowlDetail2-jcb.jpg (15.04 KiB) Viewed 2343 times

Notice the speckling on the interior in the top picture. This is where ash landed onto the glazed porcelain surface during firing. Also, the glaze color inside has been blushed a very slight bit toward the "amber" color.

On the second exterior picture, there is almost no fly ash settling on it because it is the underside of the bowl, so the piece is a more "pristine" white.

The above pot is by a ceramic artist named Bruce Wood from here in NH. He is a friend and has been a student of mine in the past. I helped him design his noborigama. This bowl is from 1980.

best,

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

[betta]

John, many thanks for the pics. I've never seen such wood deposits before. Interesting