Are you planning to buy hand made ceramic tableware? I
Sometimes, clients ask for details and friends for advise on how to acquire skill in buying hand made ceramic tableware.
Here some simple directives that not only will protect your inversion, but also will give you much satisfaction.
Some points of view concern aesthetical criteria, others concern technical skill.
It is true that studio potters usually do not have the sophisticated quality control devices available only in big ceramic factories. Yet, whether you make ceramics or you want to buy some, there are some details to take care for when buying or doing ceramics for daily use and they do not need the use of sophisticated installations, on the contrary, they may be neglected in mass production belts.
In the States, I am told that more often than not, most studio ceramicists fire to cone 6 this meaning:
2194 to 2295˚F, or 1201 to 1257˚C
Here in Japan most of us fire to cone 9 to10, this meaning:
2282 to 2300˚F or 1250 to 1270˚C
“Raku” firing techniques going as low as 1472˚ F or 800˚C, very much identified with Japanese ceramics, was a technical procedure kept in secret and used exclusively by a family or clan of potters.
This is a very famous story: the chief of the clan was forced to make an exhibition of the firing technique by no less than imperial command to a foreign legation. In exchange, to keep the family monopoly, the Emperor himself forbade the Japanese to make Raku especially with commercial purposes. The technique became very popular abroad and it was illogical, to say the least, that only Japanese could not practice it, so prohibition came naturally obsolete and at present any body can do Raku, but in Japan this ware, out of tea ceremony, is not much used for tableware.
Up to cone 6, I think we may call it “earthenware”, from 6 to 10 we call it stoneware.
Porcelain may be fired between cones 9 to 10 and much more. Yet at present in the states you can buy porcelain clay to be fired to cone 6.
What is important about temperature of firing?
At low temperatures, clay preserves its porosity it is not completely impervious to water. So it can be said that at high temperatures glazed tableware is cleaner and easier to keep it that way. Lead and other poisonous compounds leach and contaminate food much more easily when firing temperature is in the lower rank. Fortunately the use of lead and cadmium are forbidden in most of countries. Lead volatilize at high temperature so it is not used for the dosing of high temperature glazes.
Any object expanse or shrink with change of temperature. When this change is sudden, as is the case of a room-temperature piece placed inside a hot oven, we talk about thermal shock. The piece expanse with heat, then, finished the baking and out of the oven the ware cools suddenly shrinking back to its original size. These changes are not visible to the naked eye but stress for ordinary clay can break it. Ovenware is made from special clay able to resist these changes of temperatures seldom going up to 752˚ F or 400˚C.
similar, while others, specially stews are mostly cooked on ceramic pans.
If you place a room-temperature ceramic pan on direct flame, you are producing a big thermal shock: from room temperature to up to 700˚C or more if the combustible is gas. Ware able to resist this change of temperature is specially dosed with petalite, a natural compound having a very small shrinking coefficient. Not only the clay, the glaze covering it has also to be specially dosed.
Flame ware, be it ceramic or iron casted, when used for the first time should be washed with boiling water first, carefully dried in the outside then placed on low flame and warmed up gradually, let to boil disposable vegetables for let us say more 20 minutes, cooled down naturally, vegetables disposed off, washed with warm water and well dried, Then, it is ready for use next time. Every time they are used, ceramic hotpots should be dry in the outside, gradually warmed up and never let to warm up empty. Handles have to be big enough as to be able to lift the hot casserole (with gloves) without danger of accidentally spilling the hot content. The lid knob also has to have same qualities.
How do you know if a piece can resist these thermal shocks?
The only way is to ask the potter and request his or her advise on the way of using it. And this is also true for mass produced ware.
What about the microwave range?
Every day, we take ware out of the freezer into the microwave to warm up its content. Also still hot food is placed in containers, lidded (a never do-it for plastic lids) and placed inside the freezer.
Now you know that you are submitting the ware to successive thermal shocks, these may not be as bigger as for ovens or direct flame but easily go from near 0˚ to 100˚ for boiling liquids.
can be somehow different from the other.
If you love a piece of ware and want to keep it forever, be prudent with those temperature changes. Generally speaking, earthenware stands better microwaves. Porcelain not so: If warmed up in the microwave range, the piece be it earth, stone or porcelain becomes as hot as for you not being able to touch it: stop using it for microwave.
Enameled ware should not be used in the microwave.
The drawing above is after a project for a “donabe” a Japanese hotpot cooking pan made by my teacher, prof. Takahata Hiroaki. Small in size is for up two persons.
Copyright©Celina Clavijo Kashu2011 for Forum Artistico
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