Friday TeaDay 5/14/10 Material guys and gals?

[JBaymore]

I suppose "ceramic" is how most people would describe them, but I'm not sure what the difference is between ceramic and porcelain. And isn't bone china just a particular style of porcelain (thin, white, high quality)?

Porcelain, when it is fired, becomes a "ceramic" material, just like all other clay-based products.

Bone china is an interesting clay body. It takes its name from the high inclusuion of Bone Ash (impure calcium phosphate obtained from.... you guessed it... burning bones). The bone ash and the traces of phosphorous pentoxide allow the development of a very "glassy" clay body. Hence the serious translucency.

An interseting note here is the firing process for true bone china. Becasue of the high level of glassification, many of the the pieces will totally warp and deform when they are fired to maturity. So they are typically fired to the maturity temperature held in refractory "molds" that support the unglazed forms. Then the already virteous, translucent body is glazed and re-fired to a lower temperature to fuse the glaze onto the pieces, but not cause the unsupported piece to deform in the kiln.

best,

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

[Chip]

Interesting John. We hear the term clay used so often in teaware, then hear ceramic in a seemingly different way. But rarely is it stated so simply. Thanks for the enlightenment.

Then what about stoneware????????????? Please do tell. Thanks.

Well for me personally, Hagi clay transformed to hagi ceramic ... it seems. This is the weapon of choice more times than not, and almost every japanese tea is currently enjoyed in Hagi.

It just seems right! Feels right for the tea. And even tastes right?!?!

Since I got them a few weeks ago, I have been drinking from them at least 90% of the time. And now I have not drunk from them for two days. This is very hard, to be away from my new 'babies' for so long!

And who says teacups don't make a difference? Well, we all likely have at some point, til we discovered this is not the case.

[Poohblah]

Glass, :/ It's cheap and easy to find in the correct size.

At the local teahouse there is a gorgeous teaset made out of jade I don't know how well it brews tea, but it sure is a looker, especially under the sunlight. Of course, it costs five hundred dollars.

[JBaymore]

Then what about stoneware????????????? Please do tell.

Chip,

"Stoneware" is a bit of a "loose" term. It is any ceramic clay body that fires to a hard, dense, stone-like product usually at elevated temperatures in the 2100-2400F range.

You can have dark stonewares..... mainly due to the contamination of the clay materials with oxides of iron..... or even a white stoneware.... mainly made from the same constituients as a porcelain, but in a different percentage composition so that the level of fusion of the body is lower.

The whole clay continuim is not as firmly divided into precise categories as one might like to have it. As composition is shifted... a white stoneware can get closer and closer to being a "porcealin". A iron bearing stoneware can move toward having characteristics normally associated with earthenware. And earthenware can start to tighten up and resemble the porosity of a stoneware.

At a really technical level, "true" porcelain is composed of a blend of materials that are not typically used in the west. A white primary clay kaolin and a rock called, in English, something pronounced like "ptunse". So based on that thought, "real" porcelain is not often made by potters outside asia today. I know of no commercial supplier in the USA that sells ptunse as a raw material.

best,

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

[Chip]

Thanks John ... and bisque ware ... however it is spelled?

[JBaymore]

Chip,

"Bisque" (or the older and more European "Bisquit") refers to the first firing of a piece of work that hardens the clay enough for the application of glaze and/or other decorating materials to the surface.

Bisque-ing is a relatively new process, not traditionally used much before the Industrial Revolution. It allows a less skillful handling of a piece for the application of liquid glaze. This allowed relatively unskilled labor to be hired in commercial potteries to take over the separation of labor tactics that were so typical of industrial approaches. Glazing un-fired wares (usually called "green-glazing") is a REALLY difficult proposition...... and requires a lot of skill.

Today it also allows for some complex handling of surface decoration that would be difficult to impossible with "green glazing".

Most bisque firing for all types of clays is done in the 1500-1900 F temperature range. At this point, the clay is usually rather porous, like an earthenware flower pot, so that the clay will "suck in" water...... and thereby deposit a layer of powdered glaze material on the surface when dunked into a glaze slurry.

However, like I described for the bone china example above, sometimes in specialized processes.... bisque firing can actually be higher in end point cone / temperature than the "finish" glaze firing.

In the field of ceramics, the correct answer to ANY question is, "It depends."

best,

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

[Chip]

Heh, when I did this topic last night, I had no idea it was going to be an education topic. Thanks for lending your expertise, John!

BTW, TD began with Sae Midori from Yuuki-Cha. SweeTea was front and center for a taste while Pyrit and Fuji visited the TeaTable this morning.

Next up, a tasting of the Masters Collection TKY.

[artmom]

Absolutely fascinating, John! I love learning about how things are made.

The only ceramic work I ever did was on molds. I actually won a blue ribbon at the Florida State Fair for a very large ginger jar that I carved a floral decoration on and then glazed and fired. But I am familiar with the terms bisque, slip, etc.

[CynTEAa]

Glass for me as a go to vessel. I have these chunky glass teacups from a set my parents had back in the 70's. Just love them.

But I do love the Hagi clay transformed into ceramic for special moments.
And porcelain for when I feel refined.

And Yixing - love Yixing...

[LauraW]

Yunnan Noir all day at work. Is anyone really surprised? Just put some Snowbud in a thermos to take to a friend's house - I need it, after this week. It's been a long one!

[Victoria]

Adagio Masters Collection Pouchong this afternoon.
And a big box from Adagio to dive into tomorrow, yay!

[murrius]

C'mon! No votes for styrofoam?

I mostly use clay teaware with glass coming in second. I got my shincha order from OCha today so I will be in my glory tomorrow morning.

[Chip]

C'mon! No votes for styrofoam?

I mostly use clay teaware with glass coming in second. I got my shincha order from OCha today so I will be in my glory tomorrow morning.

Cooool ... maybe that means mine is reallllly close too. I received one O-Cha order this week, but have been holding out for this one since I am anxious for the new YM. I want to open that immediately.

Maeda-En 88 Nights Shincha trial tasting this evening.

[Skippyandjif]

I mostly use porcelain, with glass coming in a close second. All of my tea vessels are secondhand, so I have quite a motley crew. They're all unique, though-- I don't have any sets-- so it's pretty neat.

Started the TeaDay really late (at dinner... ) with some genmaicha. (I was moving out of my dorm and then travelling all day.) Currently drinking some lovely longjing. Mmm.

[Chip]

Also broke open Maiko Kinari. Tastings tomorrow!