History and Process of Pottery Part 2

Process of Making a Pot II
Once the pot is formed, it is put into a kiln for a bisque firing. This initial firing of the pot is to hold the shape and make it easier to decorate, and is usually at 1800 degrees Fahrenheit or higher. Some pieces are finished at this point, but many are glazed. Glazes come in a variety of colors, and each needs a specific temperature for the chemical reaction to occur that binds the glaze to the clay and turns it to glass.
The many ways of covering a pot with glaze is a big part of the artistic aspect to creating a pot. If applied thinly it lets the color of the clay show through, or thickly makes the finish smooth, but doesn't allow as many fine details to show through. Glaze can be painted onto a pot, a pot can be dipped in glaze, and creative artists will find a variety of interesting ways to apply the glaze that give different effects to the final piece.
A piece can be fired many times to achieve different effects. Some artists like to paint only in certain places, fire the piece so the glaze melts into glass, and then once it cools paint more over that and fire it again, repeating until they are satisfied. This can create different textures and very unique designs.

Defects in Pottery and Glaze
With such an involved and complex process to making each individual pot, it's not uncommon for there to be defects in the finished piece. There can be too much air in the clay, an incorrect mixture for the glaze or clay, too hot or too cool of a kiln, opening the kiln too soon or too late after firing is complete, using incompatible glazes, the amount of glaze used or even simple human error can all have a massive impact on how a ceramic or pottery piece looks once it is complete.
When clay is fired in a kiln it shrinks by a significant amount because of the loss of water. Glaze is typically engineered to shrink or expand as well, but sometimes the shrinkage of the clay doesn't match that of the glaze. This can result in crazing or peeling of the glaze. Crazing results when the glaze shrinks more than the pot, and results in spider-like cracks in the glaze, but not the pot.

Image from http://auntjemimacookiejars.com/what-is-crazing.html

Peeling or crawling of the glaze results when the pot shrinks more than the glaze, so the glaze loosens or flakes off all together.

Image from http://www.pottery-magic.com/pottery/glazes/glaze-defects.htm

The temperature of the kiln can cause bubbles, pinholes, blistering, burning and many other problems if it is too hot or too cold. If water is introduced to the kiln while it is still hot, it can cause the surface of the glaze to turn milky or hazy. Talented and experienced artists will know how to avoid these faults in their pottery

Other Methods and Pottery Safety
There are many different ways to achieve a finish a pot aside from using a powder or liquid glaze, and one such now out of use process is called Salt Glazing. Salt glazing is when common salt is thrown into a kiln at high temperature, which causes the salt and the silica in the clay to react to each other. Salt glazing is no longer in use because, while it was popular for some time, environmental cleanliness initiatives stopped most production with this method.
The selection of glaze determines how the pot can be used. Some glazes, while nice for decoration and beautiful to look at, would be toxic to eat from because of chemicals that would leech into food and be harmful once ingested. These chemicals are safe to be around and, with precautions, safe for the artist to work with.
The highest regulated hazardous materials in glaze are lead and cadmium. When buying pottery or ceramics, try to keep in mind what you intend to use it for. If you are looking for a dish to eat or serve from, be sure that the piece is considered safe to eat from, and if you have a ceramic dish, never clean it in a dishwasher. Many glazed pieces will have spots with no glaze, where they were rested inside the kiln, and these spots will let water into the clay, which will crack or crumble.

If you are interested in finding out more about ceramics and pottery or about artists who work in clay, do research! Contact your local pottery guild, or here are a list of artists to get you started!

Beate Kuhn - German
Heo Jin Kyu - Korean
Janis Mars Wunderlich - American
Halima Cassell - British
Maria Geszler-Garzuly - Hungarian
Shao Ting-Ju - Taiwanese

History and Process of Pottery Part 1

History:

The oldest ceramic piece known to man is the Venus of Dolní Věstonice, discovered in the Czech Republic. It was discovered in 1925, and is the first evidence of clay being fired to produce a hardened product. The Venus is believed to be at least 12,000 years older than the oldest pieces of pottery, which are from ancient Japan around 12,700 BCE.

These first pottery pieces are from the Jōmon, rope-patterned, era of Japanese history, named for the rope patterns that were pressed into the clay of the pots before being fired at between 1000 and 1600 degrees Fahrenheit.

Early glazes were made from ash, tin and celadon. Modern glazes are made primarily from crushed glass, clay and flux, a compound that adjusts the melting point of the materials.

Ceramics v Pottery

There is no true difference between ceramics and pottery, except in the ways the words themselves are used. Both ceramics and pottery are formed from a type of clay and can be glazed or not, though most modern pieces are usually coated in some type of glaze. Often, ceramics refers to the art of using clay on the whole, where pottery usually refers to less refined pieces, or pots and other containers.

There are three main types of ceramics or pottery, earthenware, stoneware and porcelain. The differences between these make for very different types of products. Earthenware is more porous and fragile after firing, stoneware is thicker, sturdier and more for everyday use and porcelain, held up to a bright light, is actually slightly transparent. All the different kinds of clay need different conditions for firing, different glazes and have different uses and ingredients.

Process of Making a Pot

Every pot, no matter what it's made from, starts with clay and an artist. There are many different methods to forming a pot, one of the earliest of which is the coiling method. Clay was formed into thin pieces, then pinched or beaten together into the shape of a pot. Sometimes the unfinished pot would be placed on a mat so the artist could turn the mat instead of walking around the pot to add more to it. It is believed that this is where the idea of the pottery wheel came from. The earliest pottery wheels were called Tournettes, and started to be used around 3500 BC. They were operated by the artist themselves, by pushing the wheel with a hand or foot while they worked, and were extremely slow. Faster wheels were developed soon after, as well as the technique of throwing pottery, a technique still used today by artists usually with a motorized pottery wheel. If you are interested in seeing a demonstration, this is a good example from youtube:

http://www.youtube.com/watch?v=x1RvYQJneRE

Come back in a few days and I'll continue to discuss how pots, such as those in our Ceramica Mundo collection, are created. If you would like to know more about anything I discussed or if you have any requests for topics I should cover, please feel free to email me at orders@sanmigueltradingco.com. As always, if something interests or confuses you, research! I am open to discussion of any type and I would love to hear from you!

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