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Glaze Without Fear

By Ihada Vishun
February 23 2009

 

PREFACE

About us
Carol Marians has been a potter since 1952 when she discovered clay in a craft course. She proceeded to earn two Ph.Ds. from MIT, one in Math , the other in Materials Science. Self-trained in clay, she studied the literature and took workshops with F. Carlton Ball and Tom Coleman. She has published in Ceramics Monthly and on the web site: http://vickihardin.com/articles/index.html She currently is devoting her time to the study of glaze.

Lili Krakowski started potting in 1949, graduated from the School for American Craftsmen , R.I.T. in 1953. A studio potter she has been a frequent contributor to Ceramics Monthly and Pottery Making Illustrated.

She wrote "A Basic Internet Glaze Course" published on ClayArt and http://vickihardin.com/articles/index.html.

The two have teamed up on this project, being posted under the pseudonym of Ihada Vishun.

MAKING YOUR OWN GLAZES.

INTRODUCTION
"Any new technology, if sufficiently complex, is indistinguishable from

magic", wrote Arthur C. Clarke. We might say: "Compounding glazes

is indistinguishable from sorcery". Or so it might appear to newcomers who took a first course in pottery.

Potters make their glazes from ground-up rocks, bought pre-sorted, cleaned, segregated and ground into powder. The whole process really is an exotic form of cookery. Grandmother's Putterkuchel was a sublime confection of feather-light pastry laced with cinnamon and sugar, a pinch of this, a handful of that, poke and prod as it goes. She never passed on the recipe! We are left to reconstruct it--basing ourselves on our own knowledge of what flour and butter do, what eggs do, and so on.

Many masters of the pottery craft work their glazes in this manner, mixing and blending, baking the result in the "oven". The baking is called 'firing' by potters, and the oven is called a 'kiln'. What potters do is rather simple science and technology. The actual scientists among us take it from there, and work on such sophisticated projects as designing nose cones for space ships!

This course intends to teach the basic, fundamental principals of glaze technology. It deals with the materials, what they do/don't do, and firing. It deals with glaze faults, their causes and cures.  We suggest you read "Basic Internet Glaze Course" along with "Glaze Without Fear"

Glaze is a cousin of glass. A principal difference between the two is that glaze contains alumina, which contributes to sticking the molten glaze to the pot. Glaze is not essential. Many beautiful, unglazed clay works have survived for centuries! Many are being made now! The notion that all clay MUST be glazed is wrong.

We glaze to make an object more cleanable. Food-related ware, other functional objects, "need" glaze. So do outdoor objects; bird baths, sun-dials-- as anyone who has tried to keep them clean can tell you!

We glaze to make pots more beautiful. Glaze makes pots more appealing to the eye as well as the touch. Many pots are no big deal in and of themselves, but become magnificent attired in sumptuous glaze! Most pots--plates, vases, bowls--really are pretty much the same. It is their decoration, their glazing that sets them apart. And many splendid potters mainly address the beauty of glaze.

Much of what is said about glaze bypasses functionality and beauty and focuses on the SKILL of glazing, because great skill, and knowledge is needed to design glazes, apply, and fire them well. Reduction and vapor glazes require a masterly hand. Raku also demands firing and handling skills. Oxidation fire in a fuel-burning kiln, and neutral fire such as electric kilns give, require less physical skill, but as much knowledge. The recent addition of digital controllers to electric  kilns allows their heating and cooling to be manipulated for specific effects.

Glaze is fascinating . Many potters are more interested in glaze than in clay proper. Neither interest need be exclusive . Most potters combine both to their satisfaction. (And there have been cases---of which Gertrude and Otto Natzler probably are the most famous potters working as a team. One made pots, the other glazes.)

WORK BEGINS
If glaze qua glaze is not for you, stick with the commercial ones. There are a plenty of excellent, reliable, well-tested glazes on the market; certainly more than enough to meet common need. The higher cost per pot is offset by not having to make a major investment in materials, and space. Learning about glaze, mixing one's own, experimenting with glazes. Developing recipes takes time and money. We warn about this because too many dash in without considering the full measure of what is involved.

The needed glaze materials cost $4 a pound and up. The materials are costly, and the total investment is large. You need a fair amount of each material, or the shipping costs alone will "kill you". Suppliers give "price breaks" for larger amounts, but the savings are not major ’till one buys a whole 50 lbs bag. Ideally you can fetch what you need from a nearby supplier. Which still involves time and money. (There are not that many large suppliers, and the small "local" ones need to pass on their transport costs.)

WHAT YOU NEED TO YOU MAKE YOUR OWN GLAZES
SPACE: A glaze "pantry", " cupboard" , or "room", takes space. Not just any space. The corner of your bedroom ideal for exercise equipment will NOT do as glaze space. Nor will a corner of den or kitchen.

A GLAZE PANTRY MUST BE: very cleanable, draft and breeze free; NOT a space people need to walk through--as a hallway would be--well-lit, and (our guess) a minimum of 6 ft x 6 ft floor space. You need an easily washable table, a washable floor, lots of shelf space. You need a sink and some sort of water supply. In one of our studios the sink drains into a bucket, and the water is supplied by bucket. Running water is nice but not essential. Fifty pound bags of material must be stored in solid containers such as garbage cans. These will fit under tables, but are about 20" across. Smaller quantities of material can be kept in coffee cans, plastic gallon "mayonnaise" jars, or 5 gallon buckets. These can be obtained free from restaurants, school, hospital or other cafeterias. The coffee cans are 6"x8" and the jars 6" x 10". So you can figure out the shelf space you need.

You need a scale. Much discussion of which is better--digital or regular. It does not matter. The scales sold at ceramic supply houses are costly. You can find a perfectly good scale at a baking or kitchen supply store, on the Internet--or a thrift shop. An old-style baby scale is not great for tests, but wonderful for weighing out larger batches of glaze.

The following applies equally whether you are working with clay, glaze, the materials, wet or dry --or "simply" cleaning the room.

You must have:

A PROPER RESPIRATOR, bought from your clay supplier, who will know the right kind. There are respirators just for dust, others for toxic fumes (such as those from lusters). While many potters make do with paper dustmasks, the correct respirators --kept in good condition--are the ones to use.

You need sets of clothes kept entirely for your pottery work. These should be smooth and easy to wash. Scrub suits are ideal. Washable shoes--such as garden clogs--that NEVER leave the glaze room are needed. Remember: your work clothes carry dust, they should stay IN your work area, being put on and taken off in the room. Ideally you put the clothes you take off into a plastic bag wet on the inside, or in a bucket of water for transport to the laundry-room, where the clothes will be washed  by themselves.

You need: diverse plastic containers, scoops, and permanent waterproof markers. You need buckets and sponges, note-taking equipment, a calculator but that comes along below.

Shopping List: For starters you want 5lbs of:

Ball clay (In the US Kentucky Ball Clay OM#4 is the "standard".
But other ball clays are as good.)
Kaolin (China Clay)
Flint (silica)(quartz)
Whiting
Dolomite
Nepheline Syenite
Potash Spar
Bentonite
Zinc Oxide
and 1 lb of Tin Oxide
Zirconium Opacifier (sold under different trademarks)
Titanium Dioxide

Smaller quantities of the opacifiers are included as you need all three to really learn their differences in glaze. Soda spar has been omitted, as have colorants. Nepheline Syenite will substitute for Soda spar. Colorants are costly and not needed at the beginning. Cobalt is the most expensive. Leave colorants out of your original order, and buy them when you have some glazes "nailed down", and KNOW you really want to continue in glaze.

You should have 25 lbs of three clay bodies OTHER THAN THE ONE YOU ARE USING TO MAKE POTS. These are your controls. It is on these “other” bodies that you double check your glazes.Application to different bodies also helps in finding cures for glaze defects.

REALITY CHECK BEFORE YOU READ ANY FURTHER:
Find your space. Figure out what you need to buy or build. Check the cost of hiring carpenter, plumber, etc. If you are renting space, get written permission from the landlord for rebuilding, modification, or installation of your equipment. Remember: the wiring or plumbing you put into rented space stays behind if you move. Remember: any damage caused by your rebuilding, installation etc is your responsibility.

Consult your dealer and figure out material costs.

Check regulations, zoning, fire laws, insurance before doing anything about a kiln. (Discussed below).


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