Salt Glaze Ceramics

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Salt Glaze: Some Historical Notes 3 Marvin D. Schwartz

Contemporary Salt Glaze Ceramics 9

Salt Glaze Process 13 Don Reitz

The Pollution Aspects of Salt Glaze Firing 18 Charl es Hendricks Don Pilcher Crock. Late 19th Century. G. W Fulper & Bros., Flemington, N.J. Decorated by John Kunsman. Collection, The Newark Museum, Newark, New Jersey.

2 Salt Glaze: Large simple jugs, elaborate tankards, and delicate teapots Some Historical Notes are among the objects that were made of salt glaze or salt glazed stoneware when it was in its prime between 1500 and Marvin D. Schwartz 1800. Examples ranged from the purely utilitarian to fashion Lecturer, Metropolitan Museum of Art able decorative pieces. The salt glaze body could be thin and white or grey, or thick and brown, depending upon needs of the moment. Not as easily made as earthenware, nor as difficult to produce as porcelain, salt glaze represents a popular useful product that was important over a long period. The origins of salt glaze can be traced back to Germany where it was developed some time before 1500. It was intro duced during the period when majolica was coming into fashion in Italy, but the contrast between the German and the Italian

Crock. U.S., 1841. Collection, The Newark Museum, Newark, New Jersey.

Vase. Clay Crafters, North Carolina Potters. Early 20th Century (purchased 1927). Collection, The Newark Museum, Newark , New Jersey. 3 Teapot with lid. English, Staffordshire area. Circa 1750-1780. Collection, The Newark Museum, Newark, New Jersey.

4 efforts is striking. Italians used a familiar traditional ceramic Although no real tradition for producing fine salt glaze was body, tinglazed earthenware, while the Germans devised a established, it did become an important medium for functional technique for producing a non-porous ceramic with a new kind wares in the 17th and 18th centuries. Tavern mugs, jugs, and a of glaze. Majolica designs were in the latest Renaissance number of other containers were made of thick salt glaze in grey fashion; salt glaze forms were based on medieval models but or brown with occasional additions of blue or purple decoration. decoration was generally up-to-date. Once securely established in the Rhineland, the technique Salt glaze was used by German potters for useful wares and spread to other parts of the continent and to England. for examples decorated with rich relief or intaglio patterns. The Excavations at Colonial Williamsburg have turned up both fashionable pieces reflected the German approach to the German and English salt glaze mugs. Renaissance in designs that combine realism and classicism Toward the end of the 17th century efforts at producing in a way reminiscent of Durer. Mythological scenes, and porcelain resulted in the manufacture of a second phase of naturalistic representations of forests were two of the subjects found on salt glaze.

Platter. Tea caddy and lid. Staffordshire. English, 1750-1755. Staffordshire area. Collection, Circa 1750. The Newark Museum, Collection, Newark, New Jersey. The Newark Museum, Newark, New Jersey. delicate salt glaze. John Dwight made this porcelain-like salt confused with porcelain if its orange-rind texture was not glaze in the 1690s at an English pottery. Salt glaze later was noticed. Chinese porcelain was a major inspiration for the salt consciously employed as a substitute for porcelain. English and glaze forms that were in fashion between 1720 and 1780. French potters made a fine , thin, white salt glaze that might be The utilitarian salt glaze of the 18th and 19th centuries is best known in American examples. The first efforts dated as Tankard. Circa 1700-1755. early as the 1730s, but the more familiar efforts date after the Germany. Revolution. Examples vary from those thrown on the wheel Collection, and in traditional shapes to those cast in molds in distinctive The Newark Museum, Newark, New Jersey. forms of the 19th century. Timeless designs are mixed with those th at reflect the classical interests of the late 18th and early 19th centuries. Blue and scratch decoration were applied to the American examples. Again, classicism is a factor, but so is

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Crock. Molded applied decoration in relief. Probably U.S. late 19th Century. Collecti on. The Newark Museum, 6 Newark, New Jersey. a primitivism that became one of the most charming aspects Falke, Otto von, Das Rheinische Steinzeug. Berlin. 1908. of 19th century art. ~ a nnover , Emil (edited by B. Rackham) . Fine or utilitarian, salt glaze has a definite esthetic that puts ~/ 'po tt e ry and Porcelain. 3 vol. New York or London. 1925. it apart from either earthenware or porcelain. It has been a Mounttard, Arnold R., Staffordshire Salt-glazed Stoneware. field of great variety. It should be a source of strong inspiration. New York: Praeger Publishers, Inc. 1971. Schwartz, Marvin D. , Collectors' Guide to Antique American References Ceramics. Garden City: Doubleday & Company. 1969. Barber, Edwin Allee, Salt Glazed Stoneware. Watkins, Lura W., Early New England Potters and Their Garden City: Doubleday, Page & Company. 1907. Wares. Massachusetts: Archon Books. 1968. ~ Blacke r , J. F., The ABC of EnglishSaltglaze. London. 1922.

7 Sculptural forms by Don Reitz. Hand built, salt glaze ceramic. (L) 23W' x 9\4" (R) 24" x 9\4" Contemporary Salt Glaze Ceramics Artists included : William C. Alexander Kenneth Ferguson Jim Makins Donald Reitz Ralph Bacerra Ron Garfinkel Tim Mather Byron Temple Donald V Bendel Karen Karnes Donna L. Nicholas Jack Troy Thorn Collins Steven Kemenyffy Mary Nyburg Betty Woodman Nancy Dudchenko George Kokis Donald Pilcher Mikhail Zakin

Covered container by Don Pilcher. Wheel thrown and hand built surface, tin chloride fume, salt glaze. S \14" x 14"

9 Container by Betty Woodman. Wheel thrown, salt glaze ceramic. 12"h xii" dia. Wall sculpture by George Kokis. Wheel thrown, salt glaze, painted ends, formica base. 29 ¥.t " x I OW'

Mugs by Ralph Bacerra. Wheel thown, while and blue porcelain, salt glaze. 4 \12 " x 3"

Salt Glaze Process Don Reitz Professor of Art University of Wisconsin, Madison Why does one put himself through the hassle of salt glazing? Novelty, a new point of departure, climbing on the bandwagon, because it looks like fun-these are some of the reasons. But'the main reason is simply that the object demands it. In one's aesthetic judgment salt fire is the best to give visual reality to an idea. The object would not be successful by any other process. In my view, 75 % of all con temporary salt glazed objects do not succeed because the object has nothing to do with that type of fire. One of the great qualities of salt firing is its ability to reveal rather than conceal the clay. All the beautiful scars, finger marks, scratches, and undulations of the clay are enhanced and become a signature. The forms gain a free spontaneous feeling that is impossible to achieve by any other fire. Cold and hot spots in the kiln, fire flashes, sodium build-up, and even drips from the kiln itself can add beauty. Salt firing is challenging, exciting, and unpredictable but most of all it is a way of life.

Process Historically, salt glazing was used extensively in Europe from about 1500 and later in the American colonies up to the early 1900s. It was a simple and inexpensive means of rendering clay products waterproof and achieving a glassy surface. The studio potter as well as industry employed this technique on such products as crockery, mugs, vases, sewer pipe, roofing tile, building brick and tiles, bam gutters, acid and dye jars, laboratory equipment, etc. Within the last six years it has enjoyed a rebirth via the artist! craftsman. Salt glazing has been revived in the U. S. in much the same manner as raku: the artist/ craftsman has taken an old process and set it free to develop and grow to new maturity. As in raku, technological advances have had little to do with the revival. The craftsman's thirst for discovery, experimentation, and redefinitions have been the life force. The present unlimited color possibilities in salt glaze illustrate this experimentation, for in the past salt glazed products were always brown, gray, buff, or occasionally blue. The process itself is rather simple: ware is placed in a kiln, fired to its mature temperature and common salt introduced into the kiln. The salt (chemically, sodium chloride) melts and volatilizes. Silica in the clay attracts sodium to form a glassy silicate on the surface of the ware. Chloride changes to chlorine gas in the kiln. As it leaves the hot kiln it combines with hydrogen in the air and becomes hydrochloric acid. This acid is a serious concern discussed under "kilns:' Colors are produced by the types of clays, slips and stains used. Salt firing may 13 be done from cone 04 to cone 12 depending on the clay body and 72" high inside. It is a sprung arch kiln. I feel this gives more load desired effects. space. Any type of kiln construction wi1l work. Analyze your needs and Kilns the dimensions of the kiln wi1l follow. After one has examined the pros and cons of salt glazing and gained There are many types of bricks on the market and I have used many knowledge of the process, the first step is to decide on a location of them. (Go to any brickyard and ask.) Selection of bricks depends on for the kiln. Ventilation is a principal concern. The hydrochloric acid how long you want the kiln to last, how many bricks will be needed, produced during firing is a real problem, particularly to the person and the cost per brick. Insulation brick, even the so-called "salt salting. Breathing this vapor is not good for you. It will etch window repelling" brick, are short-lived because they are porous and sodium glass, attack most metals and draw letters and phone calls from will attack them. For this reason, I use A. P. Green Clipper brick. your neighbors, not to mention a visit from the local fire department. These are a top quality refractory brick, relatively uniform, have For these reasons I live 10 miles out of town and 2 miles from my a lower iron content, hold up under heat, sodium and flame impinge nearest neighbor. This is not to say that salt firing cannot be done in ment, and are reasonable in cost. High alumina and mullite bricks town. By researching elaborate exhaust systems and water baths, are available, but price can make them impractical. I mortar my bricks and checking your neighbors and local clean air laws, salt kilns can because the sodium buildup on the interior of the kiln will pun the be operated. The main point is always ventilation. brick in. Selection of mortar is important. A high alumina mortar should The following directions are based on my experience working with be used ; a thin wash coating is sufficient. Satanite, an A. P. Green the salt process. They are given as information and not as a bible. product, is very good. Arco 70, a Grefco product, works well also. Each person in his own situation will expand, adapt, and add to it. The most cricital part of the kiln is the firebox (which is also the The size of the kiln is rather important and is determined by several most logical place to introduce salt). As the salt lies in the firebox factors: scale and quantity of work, availability of materials, kiln in a molten mass before volatilizing, it erodes the brick and runs shelf size and kiln purpose. For example, I wanted my kiln large enough under the bag wall, melting the pots on the floor. It flows down between to give a payload but not so large that I could not fill it two or three the bricks as fast as you put it in, or runs back out the burner port. times a month. With this frequency of firing I can see results faster, do You can solve all this by doing three things. Make the floor of the more experimental work, and analyze what is happening. I had a firebox lower than the floor of the kiln. Line the firebox with a layer of good source for hard, refractory bricks at a good price. My shelves any high alumina castable and at the same time slope the firebox were 12" x 24". The purpose of the kiln was to make a total commit floor away from the burner port. See illustration 1. Note that the first ment to salt, produce enough ware to earn a living and get maxi- course of bag wall bricks are placed on their 2 Y2" side so they mum use of fuel. Therefore, I built the kiln 42" wide, 63" deep, and extend above and below the floor. This helps to seal off the salt and

1. Fire Box Front Side View View Kiln Kiln / ']Yz" I Wall I I==;r===~==t Wall I I IBrick I. 2Yz" :======~ 1 I 9" I 1 Castable I Bag Wall I I - r- I I Inner F loor i II ... / II II II l I 1 ~ ~ I I I I ~ I II II I ~ I Cinder ~ II ~ Block 14 15 creates a strong foundation for the rest of the wall because the clay wads to set them level so they will not warp. Alternating the bricks are cemented in place by the castable. surfaces (reversing the shelf) at each firing, will also deter warping. Salt ports may be located where desired, depending on the kiln. Silicon carbide shelves are much safer. They are stronger and will I make the burner port large enough so that I can introduce salt above take a greater shock. They can be washed but need not be. Carbide is the burner. extremely reactive to sodium but by washing the shelves they are A kiln which has been used for salt firing may be used for regular protected from the attack of sodium and are given longer life. Also, reduction firing. Because the walls have been coated with sodium, with a wash on the shelf the ware can be set down without the use glazes will be altered somewhat, the most obvious result being a higher of clay wads. I wash all sides of my shelves, but the underside should gloss. I feel that firing glazes in a salt kiln can produce quite beauti have only a thin coating to protect it, otherwise it will drip on the ful effects. I do not see it as a hindrance. ware. For the underside make the wash as thick as milk, scrubbing it in with a brush. The wash should be much thicker for the top. Burners & Fuels A simple wash is made of kaolin and alumina hydrate in equal parts Virtually any type of burner and fuel will work-propane, butane, by weight. Small amounts of ball clay will help the mixture to natural gas, wood, oil, coal etc. The type of kiln, accessibility of brush easier; a small amount of fire clay will increase its binding qual fuel, and desired effects will be your guide. I have noticed no difference ity. A good quality alumina paint may also be used as a wash. This in the end product when using propane, butane, or natural gas. I seems to work best on clay shelves. There are also high alumina papers do feel that oil fire gives the ware a bit of opalescence. Wood will pro on the market as well as alumina shelves. These shelves are expen- duce ash and that too, makes the ware different. Precisely for sive but little or no wash is required and scraping is almost unnecessary. these differences I will finish off a fire for the last two hours with wood, Care should be taken in cooling, however, as they are susceptible to oil, tires, or anything else that will burn. The beauty in salt is its cracking. There are many brands on the market. I have found the unpredictability, but I feel the need to help this quality along. Those high alumina shelf by New Castle Refractories in New Castle, beautiful drips, rich blushes, variation of salt coverage, and flame Pa. to work well. impingement are 80% the craftsman's doing. If clay or silica carbide shelves are not washed, they must be scraped If propane gas is used, the size of the tank and gas pressure are impor before each use. Clay wads must be put under the ware to prevent tant. Propane comes as liquid in a tank; it must vaporize to work sticking. It is al so desirable to wad the shelf posts to keep them efficiently. In cold weather this does not happen fast enough to produce from fusing to the shelf. A mixture of kaolin, alumina hydrate, and sufficient pressure. (Even in summer the tank becomes cool, water flint in equal parts works well for wadding. However, I simply condenses on the outside and reduces pressure.) Volume compensates use my regular clay and dip the wads in a can of dry alumina hydrate. for this problem and therefore it is advisable to have as large a tank as can be handled. I have a 1,000 gallon tank at industrial gas rate rather than house rate, for it is always cheaper. Propane and butane gas are heavier than air, unlike natural gas. For this reason the tank should be placed downhill from the kiln and at least 30' from it. Obviously, no liquid gas should be indoors, for if there is a leak the gas accumulates on the floor and a careless match could cause an explosion. Most gas companies at first will want to install a low pressure regulator about 10 lb. house pressure. This is insufficient. The minimum I suggest is 35 lb. For cold weather an industrial 70 lb. regulator will be ample. Shelves, Furniture, & Washes Any kind of kiln shelf and furniture will work. Clay, silicon carbide or alumina shelves are the most common. When clay shelves are used, it is important to coat them with wash, not to overfire, and to use 16 17 Color because they burn and produce an ash, give special effects to the ware. Color is achieved by the use of slips, stains, dry oxides, washes, glazes, Bulbous forms may extend over the firebox to receive extra flame overspraying, foreign materials in or applied to the clay, place- impingement and salt buildup. By placing a piece in contact with the ment of ware in the kiln, control of the atmosphere, fuming, direction kiln wall, beautiful patterns can develop from the seasoned bricks. of flame pattern-on and on! Pieces may be stacked one on top the other with or without clay wads. Stacking one section of the kiln tight and leaving other areas open will Slips are the most common source or means of applying color. I apply direct a flame pattern. A brick coated with cobalt wash and placed in slip to the ware while it is wet. A simple base slip would be: the middle of a group of pieces wi11 give good blushing, especially where 10% rutile = honey white slips are used. 5 % iron = warm brown 60% kaolin Draw rings should be made from the same clay used for the ware in the 2 % coba1t = blue '1 15 % feldspar kiln. About a half dozen should be placed in the kiln so they can be } white + 5% iron ~ 15% flint ~ 2 % manganese ~ = black easily pulled during salting. 10% ball clay J 6% rutile ~ Firing 2 % cobalt ~ = green Firing is a simple process. At least at the start it seems to be. But the All the possibilities of decoration used in "regular" firing, from incising more you salt fire and experiment, the more you realize that firing is as creative an act as forming the objects. It is total involvement in the to applique, are possible in salt firing. This sequence, for ~xample, is typical in my work: a piece is formed, lines are incised, slips and clay salting process that counts: How you fire depends on the results you ornamentations are applied; the piece dries enough to be handled, raw want. oxides are rubbed in, washes and stains are brushed or sprayed on. Because the ware is glazed during firing, the bisque fire can be elim Glaze accents are applied and a pinch of feldspar and/ or frit is thrown inated. But if you want glaze inside a form, or if you use glaze as on the surface. The piece is then ready for the kiln. accent, then you must first adjust your glaze formula to fit either wet or dry ware. If you have problems with greenware cracking, I advise Stacking bisquing those pieces that are to be glazed, following your normal Flame impingement, blushes, and the amount of sodium accumulation bisque firing schedule. The use of a stip glaze applied when the ware is can be controlled by the stacking of the kiln. By grouping pieces close leather hard can also help to avoid cracking. together, more sodium will form on the exposed surfaces than on the When the work is ready to be fired you have to make a decision. If you protected sections of the ware. Shards placed on the ware, pieces laid want dark Ware, reduce the kiln. If you want lighter colors, oxidize. I on their sides or overlapping one another will produce shaded areas. have found that taking the kiln to cone 8 in oxidation and then going to Materials such as straw, wood, metal, banana or orange peels, etc. cone 9 with a moderate reduction works wen. When salt is introduced

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18 19 into the kiln, it will reduce automatically due to insufficient combustion. Cooling The selection of firing temperature is important. If you are using a The rate of cooling affects color. Cooling slowly usually results in dark stoneware clay at cone 8 it will salt and usually be light in color if you colors; cooling fast gives lighter color. The clay body and type of ware have not reduced. This is dependent on the amount of iron in the clay. are factors in determining rate of cooling. I usually cool my kiln rather At cone 10 the iron in the clay is very active and the ware is usually a fast. darker tone. This brings up an important point. Temperature affects When the kiln has cooled to a low red heat, fuming may be done by both the amount of sodium on the ware as well as color. It is for this introducing chlorides into the kiln. Stannous and ferrous chlorides reason that I fire my kiln unevenly. The temperature will vary from work well. They will give a mother-of-pearl quality to the ware. cone 8 to cone 10. This temperature variance occurs by arranging the bagwalls (raising or lowering them) , stacking, or controlling the bu mers. There are various methods of fuming. You can reach into the kiln with tongs and pull out a pot when it has cooled to a very low red heat, and When the kiln nears the temperature chosen for salting, you may do then hold it in the chloride fumes. For this method put a tin can on a many things to force beautiful "accidents ~ ' Wood, tires, straw and other small burner, mix the chloride with a small amount of alcohol and place combustible materials may be introduced into the kiln. Oil may be this mixture in the can. In a short time the chloride will heat and begin dripped into the firebox. Colorants in their carbonate state (cobalt, to smoke. Rotate the pot in the fumes and then put it back into the kiln copper, iron, etc.) may be added to water and introduced as a fine to cool slowly. (See illustration 2.) spray. Do not put large amounts (cupfuls) of water directly into the kiln-at high temperatures it can blowout the door, break the bricks, or If you want to fume the entire kiln, simply throw a few spoonfuls of blow the whole kiln up. Steam will also produce strange effects on the chloride into the kiln. It can be introduced into the firebox , through the ware that mayor may not be desirable depending on the forms. spy hole or directed to any part of the kiln where you want a concen trated fume. Salting In fuming there is always the risk of scum forming on the ware which Common rock salt is generally used. Some salt has calcium and/ or can be quite undesirable. To prevent this, the kiln must be ventilated magnesium added; this usually will produce a very dark color. Sodium well. The fumes should not be permitted to stay in the kiln. Open the bicarbonate or sodium carbonate may also be used. I prefer pure rock damper and firebox ports, take a portion of the door down or do any salt which works well and is cheap. thing else you can to ventilate. I usually salt when cone 9 is half over. By the time I finish salting, cone 9 is flat. Salt may be introduced into the kiln in several ways: blowing 2. Tin Can it in through a fan, making small paper packets and throwing them in, Fuming filling a pipe and pushing the salt out with a plunger, or simply throwing in handfuls at a time. If you wet the salt, the water sometimes causes a slight explosion and breaks the salt particles down to a smaller size. Theoretically the salt should then melt faster. But I prefer to throw the salt into the firebox dry, a handful at a time. There are no loud explo sions or dramatic shelf collapsings, but things work just fine and are much safer. I use about 30 Ibs. of salt over a two hour period but amount depends on the type of ware in the kiln. There is little point in containing putting more salt in the firebox than it can hold. chloride When salting, use enough damper to produce back pressure in order to achieve maximum use of the salt. The amount of damper will depend on the type of kiln and its flue size. After a few pounds or so of salt are in the kiln, take out a draw ring to see how much sodium has accumulated on the ware. By alternately salting and pulling draw rings, you can decide when there is enough salt. The draw ring is only a record of the surface of the ware, however; it does not tell you a thing about color. 20 21 A third method is to spray the chloride directly on the ware. Dissolve temperatures are cone 8 to cone] 1 but salting can be done at lower the chloride in alcohol and spray it on the hot ware with a squirt bottle. temperatures with vitreous non-talc bodies. Of these fuels, natural and Of course you run the risk of breaking the pieces but that's part of the bottle gas are most easily regulated to produce an oxidation or reduc game. Do not be discouraged if the loss factor is high, for it takes a lot tion atmosphere. The difference between these kiln atmospheres is the of practice to fume successfully. When it works, it really works well! key to controlling the color of the glaze as we ll as the polluting effluents. You can also make a wand out of a piece of %" pipe. Cap one end and In an oxidation atmosphere the fuel is completely combusted and the drill holes in the pipe. Put the chloride in the open end and hold the free carbon, hydrocarbon, and carbon monoxide by-products are kept pipe inside the kiln at different places to vary fuming concentration. at a minimum. Consequently the ware has a lighter or cleaner appear (See illustration 3.) ance and the kiln effluents consist almost entirely of water vapor and It is obvious that you should plan ahead if you are thinking of fuming. carbon dioxide. (Low grade fuels containing excessive sulphur can mar The way you stack the kiln and particularly the way you lay up your this purity.) door are important. Whatever methods, remember not to breathe the Reduction atmospheres are based upon incomplete combustion. An chloride fumes. excess of fuel produces carbon which alters the color of the iron in the clay and consequently the glaze. Deeper and richer browns are pro 3. Pipe duced in this way. A large quantity of this unburned fuel is emitted in Fuming Holes on the form of free carbon, relatively stable hydro-carbons, and carbon top half monoxide. These emissions are identical to those produced by power companies burning coal (with the exception of inorganic fly-ash), jets burning kerosene, or cars and trucks burning gasoline. Cap Salt on end While salts vary-some contain traces of magnesium, calcium, or iodine -they are basically sodium chloride (NaCI). Upon introduction into the fire at advanced temperatures when the clay body is vitrifying, the The Pollution Aspects of Salt Glaze Firing salt dissociates into sodium and chlorine. The sodium unites with the Charles Hendricks alumina and silica in the clay to produce a glaze-a sodium, alumina Professor of Nuclear & Electrical Engineering, University of Illinois, silicate. Fuel + air + salt + clay = carbon dioxide (CO;l) + water Urbana (H20) + nitrogen (N2 ) + sodium hydroxide (NaOH) + hydrogen chloride (HCI) + heat + glaze. Don Pilcher Assistant Professor of Art, University of Illinois, Urbana Some sodium and chlorine vapors are exhausted into the atmosphere during firing. These gases leave the kiln as condensation nuclei which The current intense interest in pollution has prompted many potters have an affinity for moisture and thus produce a very noticeable fog. using salt kilns to question this process as a means of production. Tn This fog is composed of hydrochloric acid and water fog droplets addition, many government agencies, especially in metropolitan areas, (HCl.H:!O) condensed on sodium salt nuclei. Tn concentrated amounts have investigated and closed down salt kilns. For these reasons we have or closed areas the hydrochloric acid vapor is highly toxic. Humans and undertaken an examination of the pollution aspects of salt glazing. steel are the most seriously affected. (Our salt kilns have been operat Hopefully our findings will give the potter and other interested parties ing for four years in close proximity to trees, grass, shrubs and some facts and solutions to the problem. flowers with no ill effects.) The following is an explanation of salt firing and its by-products. Note This hydrochloric acid fog will usually dissipate within fifteen minutes that variables may occur depending on fuels, kilns, clays, and salts used. of the initial salt introduction as the reactions terminate and as the The pollution factors of salt firing are twofold-the fuel and the salt. components become diluted in the atmosphere and the condensing drops grow large enough to fall to the ground. This fact however, does Fuel not diminish neighborly concern over the fog. Natural gas, bottle gas, oil and wood are individually capable of Since the object of salt glazing is to deposit a sodium vapor within the producing the required temperatures for saltin'g. In most cases these kiln, we recommend using other sodium compounds in place of salt, 22 23 thereby eliminating the objectionable chlorine gases. Such compounds as sodium bicarbonate (NaHC03, baking soda) and sodium carbonate (Na2C03, washing soda-sal soda) will work. This fact was noted by Cunen Parmelee in his book Ceramic Glazes written in 1948. When purchased in commercial quantities, the cost of these other compounds is not prohibitive. When using these other sodium compounds it is advisable to introduce them in small amounts over a longer period of time. In this way one can avoid a saturation of sodium oxide in the fire box and thus prevent severe deterioration of the refractories. Summary We would like to make some comparisons between kiln firing and other combustion sources common to our present way of life. Variations occur, of course, from kiln to kiln, car to car, and airplane to airplane. A 30 cubic foot kiln fired to cone 9 and salted consumes: 30 Ibs. natural gas, 570 lbs. air, 251bs. salt. The elemental constituents of these materials are approximately: 22.9Ibs. carbon, 7.1lbs. hydrogen, 114.0 lbs. oxygen, 456.0 lbs. nitrogen, 10.0 Ibs. sodium (90% of which is deposited on the ware, bricks, kiln shelves), 15.0 lbs. chlorine. This 30 cubic foot kiln produces these effluents in the final two hours of firing: 60.0 Ibs. water vapor, 84.0 lbs. carbon dioxide, 456.0 lbs. nitrogen, 1.0 lb. sodium compounds, 13.5Ibs. chlorine as hydrochloric acid and other chlorine compounds. When using sodium carbonate (Na2C03) for glazing, the reaction for complete combustion is: fuel + air + washing soda (Na2C03) + clay = nitrogen (N2) + carbon dioxide (C02) + sodium hydroxide (NaOH) + water (H20) + glaze. With the exception of the sodium and chlorine compounds, the firing of this kiln for two hours is comparable-in energy consumed and effluents produced-to a car running at 70 mph for one hour or a 707 aircraft at cruising speed for three seconds. It is not our intention to whitewash salt firing as a pollution source but to place it in proper perspective to the overall environmental picture. In this relationship, kiln firing is not a considerable pollution source. References Handbook of Chemistry and Physics. Cleveland: Chemical Rubber Publishing Company. North American Combustion Handbook. Cleveland: North American Manufacturing Company. Parmelee, Cullen, Ceramic Glazes. Chicago: Industrial Publications, 1948. Rhodes, Daniel, Kilns, Design, Construction and Operation. Philadel phia: Chilton Book Company, 1968. 24

"Mary" from the two-part set "John and Mary" by Thom Collins. Wheel thrown, kaolin slip, salt glaze. 16" x 13"

26 P-Iatter by ancy Dudchenko. Hand built. stone ware, sa lt glaze. 7"h ; 28" dia. Courtesy Scarabaeus Ltd., New York City

27 Lidded storage jar "Cherub Jar" by Byron Temple. by Ron Garfinkel. Wheel thrown, Wheel thrown, salt glaze ceramic, salt glaze ceramic, mUltiple firings. decal. l2"h; 6" dia. 91,4 "h; 7" dia. Box forms b ~I"hail Zakin and built salt glaze. ' Left to right,' 8¥-l",5 1/2" Vase by Karen Karnes. Wheel thrown, stoneware, salt glaze. 13" x 10 V2 "

30 C hess table and chairs by Donald V Bendel. Hand bui lt, salt glaze ceramic. Table 26" x 18" x 10" Chair (L)21" x 15 " x 10" Chair (R) 22" x I 5" ~ 12"

31 "Slab j " by Wi ll ia m C. Alexa nder. Sl ab construction, stonewa re, salt glaze, lu sters. 18" x 12" x 3" 32 Lidded cont~iner Teapot by by Jim MakiOs. Mary Nyburg. Wheel thrown, . Wheel thrown, salt glaze ceramic. slip decorated, 13"h: 8 V2 "dla. sa lt fired with tin chl o ride fuming . 5" X 61/2" "On a Good Day the Sun is the Landscape's Handle" by Jack Troy. Lidded box. Slab construction and hand built, salt glaze ceramic, mirror. 24" x 13" x 9Y2".

34 "Slant Wedge # 2" "Nude with X" by Steven Kemenyffy. by Ken Ferguson. Hand constructed, Wheel thrown oil fired , salt glaze. and hand built surface, 47" x 39" porcelain, salt glaze. 19" dia.

35 Untitled ;q by Tim Mather. Hand constructed, stoneware, salt glaze, flocking and cloth attachments. 28% " x 8"