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glaze
 

 

 

 

 

 

 

 

A beautiful piece of pottery is a result not only of the techniques used in creating the form, but a knowledge of glazes and skill in application of those glazes to the form. Every potter will tell you of a time when he or she was thrilled with a piece of bisqueware and totally disappointed when the piece emerged from the glaze firing.

Glazes are a combination of clays, chemicals and stains that together create colors that adhere and interact with clay during firing.  At the LMRA Pottery Studio, members of the Glaze Committee make cone 6, cone 10, and raku glazes from tried and true recipes. Mixing our own glazes is significantly cheaper than purchasing commercial glazes. Members are welcome to use commercial glazes, or their own recipes, keeping in mind the temperatures at which those glazes must be fired.

As a rule, the higher the firing temperature, the less variety of colors you will find in glazes. This is because chemical colorants and stains will often burn out at high temperatures. On the other hand, the deep, rich finishes often obtained at high temperatures are difficult to achieve with low-fire glazes.  

 


Click on a topic below for information
and hints about the various methods of
firing, and glazes available for each:     

For example, red clays contain iron and fire in cone 6 and cone 10 anywhere from a cream color to a dark metallic gray, and glazes on these clay bodies will fire darker than on white clay bodies. Porcelain contains few, if any, impurities and fires white or translucent in cone 10 and 6, and glazes applied to porcelain often fire to their true colors. The best way to determine the behavior of a glaze is to create test tiles from the types of clay you plan to use.

The studio usually keeps a supply of bisqued bowls in the glaze room that can be used to test glazes. These often yield better results than test tiles, as the size and shape of a bowl allows the glaze to pool or break. Finished bowls are donated to the Tarrant Area Food Bank for the Empty Bowls fundraiser each February.

The LMRA Pottery Activity has a total of seven kilns:

  • Three electric kilns - fired frequently to cone 06 (bisque) and cone 6 (glaze)
  • One large gas kiln - fired approximately monthly to cone 10 (glaze only)
  • Four outdoor gas kilns for alternative firing - fired as needed
 

Electric Kilns - cone 06 & 6 firings
 
 

These kilns are loaded and fired as the bisque and glaze shelves fill with work by members. Several members have been trained to use these kilns. Members are asked not to load or fire the kilns without training and approval by the President of the Pottery Activity.

Only cone 10 clay should be glaze-fired in these kilns. Because these kilns are old and frequently fired, results can be inconsistent, and temperatures exceeding cone 6 are possible, leading to melting clay and damaged kilns if a lower-temp clay is used. The cone 6 glazes used at the Pottery Activity are formulated to be fired in these kilns with cone 10 clay.

Be sure to wipe the underside of your glazed piece to prevent it sticking to the shelf during firing. If you think the glaze on your piece will run, place it on a patty (available on the brown bookshelf in the picture). If your piece requires special handling, place a note with it on the glaze or bisque shelves.

Firing in these kilns take 36 to 48 hours to complete. Depending upon the amount of time set aside for warming up, the actual firing takes 14 to 20 hours, and cooling takes an additional 18 to 24 hours. These kilns are automatic and have the actual temperature of the kiln interior displayed on their control panels. Kilns must not be opened until the temperature reads 200 degrees or below.

A note on single firing: We do not encourage single-firing (pieces glazed when green and fired to cone 6 or 10) at the studio. Bisque firing burns off most of the impurities in the clay; firing from green to vitrification may affect the appearance of the glaze. Single-firing can result in breakage and exploding pots. In a co-op setting, where each firing consists of the pieces of many members, single-firing risks too much damage to other people's pots.

kilns

Commercial low-fire glazes and underglazes
 

Most commercial low-fire glazes are recommended to be fired at cone 06. This is a temperature slightly lower than recommended bisque-firing temperatures and significantly lower than cone 6 or 10.  Two exceptions to this rule are underglazes and "Stroke and Coat" glazes by Mayco.  Several brands of underglaze can be found at local ceramic supply houses and on line.

Underglazes are colorants that can be used on bisque ware or green ware and have a matte finish after firing. A gloss finish can be achieved by applying clear glaze over the underglaze. Underglazes can be painted on or wiped back for different effects. Check the label to see how high an underglaze can be fired; many can be fired up to cone 6.

"Stroke and Coat" is a liquid commercial glaze that comes in a variety of colors and can often be fired up to cone 10 with a glossy finish.

Most of these types of glazes should be brushed on in three coats. A good method to minimize visible brush strokes is to do one coat horizontally, the second vertically, and the third diagonally.

If your intention is to get detailed colors without running, these two types of glaze will give you the best results. Using, for example, a blue cone 6 glaze to paint flowers on a white cone 6 vase may lead to running and blending of the colors during firing. Underglazes will not run or move.

Another technique to make details "pop" involves coating a piece of bisqueware with a stain made of iron oxide, cobalt oxide, or other chemicals, which will change the coloration of the overglaze. Several stains are available in the glaze room.

At LMRA, we do not customarily do glaze firings at cone 06 (low-fire). If you have a special piece (from a workshop, for example) that was made with low-fire clay, exceptions can be made. Place your bisqued, glazed piece on the BISQUE FIRE shelf in the chemical room with a note explaining the situation, AND contact Bobby or Thea.

  ladybug stars rio
Three coats of Velvet Underglaze were applied to this piece after bisque firing. The piece was dipped in clear glaze and fired to ^ 6. Velvet Underglaze was applied and wiped back, and the piece was dipped in clear glaze and fired to ^ 6. Red iron oxide wash under
^6 celedon glaze
 
 

Cone 6 glazes
 
 

Cone 6 glazes are fired to about 2230 degrees. Commercial cone 6 glazes are commonly available but tend to be expensive. At the LMRA Pottery Studio, we make all of our own glazes, with the exception of our clear glaze, which is a commercial bulk (powdered) glaze.

Cone 6 glazes can be found in the green buckets in the glaze room. They can be applied by brushing (three coats), dipping, pouring or spraying. Many look great applied over each other in layers. To avoid excessive glaze on a piece, multiple layers should be applied thinly by spraying.

These glazes must be stirred before use as they tend to settle. A power mixer is available for this purpose. If the glaze appears too thin after mixing, any dried glaze adhering to the sides of the buckets should be scraped into the mix. The glaze should be the consistency of heavy cream and can be tested by dipping a dry finger into the glaze. It should coat the finger and "break" at the knuckles. Members are asked to refrain from adding water to the glaze buckets. If a glaze is too thin, it may be ruined, as removal of water can also remove any water-soluble chemicals in the glaze. If a glaze appears to be too thick, members are asked to pour some of the glaze to a separate container and thin with water. A very tiny amount of water is often sufficient to thin a glaze. If you are unsure, ask an experienced member for assistance.

If a glaze is running low, write it on the blackboard and a member of the glaze committee will make more.

At the LMRA Pottery Studio, we require members to use CONE 10 CLAY ONLY in the Studio. This is due to sometimes inconsistent temperatures achieved in the electric kilns, and because we recycle clay scraps for use in all kilns. However, it is important to note that cone 10 clay is not fully vitrified at cone 6 and will not hold oils or other liquids over the long term. Vases, oil lamps, cruets and other items intended to contain liquid over a period of time should be fired to cone 10.

All of our cone 6 glazes are food safe.

NOTE: ANYTHING over Pumpkin Matte will cause the glaze to run in firing. Layering over Pumpkin should be done close to the rim on the exterior, or on the interior only. Similarly, Aqua Ice over any other glaze will also run and should be similarly applied.

At the LMRA Pottery Studio, we have ten cone 6 glazes available for your use (Aqua Ice best for layering, not shown alone):

 
clear
white celadon
Clear with underglaze on white stoneware Naragon White Mock Celadon
pumpkin black red
Pumpkin Matte w/ clear border Black Kemp's Red
stublu fb shino
Studio Blue (with shino) Floating Blue Shino (exterior, red interior)

Double- or triple-dipping leads to interesting combinations of color:
celoverpum celoverpum celshino
celwhite
flbluwht shinturq
multi
redpum
trans turqblu turqshin
stublupum
stublu
whtoverblck
aquaIce whitoverflblu
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Gas Kiln - cone 10 firing
 

The Pottery Activity has one large propane kiln that is fired to cone 10.   Unlike the electric kilns, which have electronic controls and can be set to fire automatically, the gas kiln must be manually controlled.   Cone 10 is required for full vitrification of cone 10 clay. Porcelain is also most beautiful when fired to cone 10 or higher.  Higher temperatures (up to cone 12) on the bottom shelves of this kiln have been frequently achieved.

The electric kilns are oxidation firing kilns, which means that oxygen is present in the kiln during firing.   Gas kilns may be fired in oxidation, but more dramatic results are often obtained when the kiln is fired in reduction, meaning oxygen is removed from the firing chamber . Many glazes fire differently in oxidation than they do in reduction.   A delicate balance of oxygen and temperature must be maintained in order to achieve desired results. Most of our cone 10 glazes are formulated for reduction firing.

A few members of the Pottery Activity have schooled themselves in the operation of this kiln (every gas kiln is different) and have been consistently achieving beautiful results.   This kiln is somewhat expensive to operate and is fired ten to twelve times per year. Firing dates are posted on the front page of the web site and on the door in the studio.  Loading is usually done on a Sunday afternoon and firing is all day the following day. The kiln is unloaded on Wednesday.

Although the kiln looks roomy, very large pieces cannot be fired in it.   The kiln shelves are half shelves, 11" wide, and must hold not only pottery but posts and cones.   Pieces with a bottom width in excess of 9" will overlap shelves and will warp during firing. Very tall pieces take up too much vertical space and tend to leave gaps in the kiln.   A full kiln fires more efficiently than an empty kiln, so very tall pieces are discouraged.
If a piece does not fit within the shelving unit by the kiln, it won't fit in the kiln. Very tall pieces should be fired in the cone 6 kiln or in the Brodnax kiln outside.

Members who wish to fire in this kiln are encouraged to help load the kiln. Helping to load almost guarantees your pieces will get into the firing!

Note: Please be aware that glazes fired in other gas kilns may not look the same when fired in this kiln. Many schools and commercial operations use natural gas kilns; this is a propane kiln and may result in different atmospheric conditions.


empty full
The gas kiln The empty kiln A completed firing
closeup cones closed
Pyrometric cones are placed in several areas of the kiln to monitor temperature The cones must be visible through
the peep holes
Kiln door showing peep holes for cones and drill holes for oxygen and temperature meters.
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Cone 10 glazes
 
Cone 10 glazes are more tempermental than other glazes and depend both on temperature and regulation of oxygen for success. At the LMRA Pottery Studio, you will find the cone 10 glazes in the white buckets in the glaze room. We have twelve cone 10 glazes available for your use:
 
  • Malcolm Davis Shino - best on darker clays
  • Pete's Red - requires heavy reduction
  • Salazar Blue - a pretty, dependable blue
  • White - glossy and opaque
  • Iron Blue - irridescent over other colors. Tends to run.
  • Nagamoto Teal - teal in oxydation, pink in reduction
  • Tenmoku - dark brown with black specks, slightly metallic
  • Spodumene - cream-colored matte finish
  • Eggshell - cream-colored with specks, browner on dark clay
  • Celadon - pale green, fires gray on dark clay
  • Black - slightly translucent. Cobalt color over celadon.
  • Ohata Khaki - earthy brown, redder over dark clay
 

These glazes vary greatly with the clay body. Five commonly used clays are shown below. All were fired in a reduction kiln. These are all cone 10 clays and were fired to full vitrification, cone 10 or above. All of the glazes are shown in the same order and you will note the great variations of color on the different clays. (A couple of tiles did not make it through the firing.) These tiles are kept in the glaze room and members are encouraged to study the actual tiles to determine what glazes to use.

Note: If you glaze a piece red, put a note with it on the shelf to let the kiln loaders know. Reds need special placement in the kiln.

All of our cone 10 glazes are food safe.


Porcelain: Bright white when fired, colors are true. These tiles were fired in reduction. N. Teal requires oxydation to achieve blues.
porcelain
Dillo: High-fire white stoneware with a small amount of iron. Fires to a nice white with small iron specks. Insufficient reduction was obtained for red.
dillo
Trinity white stoneware: High-fire white stoneware with visible spots of iron. Fires to a pale tan when vitrified.
twhite
Trinity Red Stoneware: High-fire red stoneware with heavy iron content. Fires to a warm brown when vitirified. Red got insufficient reduction.
tred
Balcones Dark: Heavy iron content, beautiful metallic brown when vitrified. Will blister at very high temperatures.
balcones

Raku and Alternative Firing
 

The Pottery Activity has two barrel-type kilns, one front-loading kiln, and one converted top-loading kiln in the yard outside the Studio.   All are fired with propane and are for pieces that have been previously bisqued.

The barrel kilns are used primarily for raku.  Raku is a method of firing whereby pieces are quickly heated and then dropped into buckets of flammable materials such as paper, hay, or sawdust.   The resulting flames reduce the amount of oxygen in the bucket (reduction firing). The flames are quenched and the pieces allowed to cool in the smoky containers.   Depending upon the glaze used, the result may be a shiny metallic or crackle finish, or a smoky matte or textured finish.

The top-load kiln is a converted electric kiln and is used for sagger and black pottery firing.   The front-load kiln was built in 2009 by Randy Brodnax and can be fired to cone 6 and occasionally cone 10, in addition to raku.   

Unlike either the electric kilns or the large gas kiln, these kilns fire quickly, and pieces may be done in as little as an hour (or three hours for the Brodnax kiln).  Because the pieces are going from ambient temperature to very hot temperatures very quickly, they experience a great deal of thermal shock.  The pieces best able to tolerate this method of firing are usually wheel-thrown using fairly groggy clay.   Very smooth clays such as B-mix do not work well in raku, although some members have had good results with porcelain.   Hand-built items will survive if they are well-proportioned, with bottoms no thicker than walls, and well-compressed.   Flat items often crack.  The Brodnax kiln is very fast but gives inconsistent results when used as a cone 6 or 10 reduction kiln.

Because there is a risk of serious injury when operating these kilns, members are prohibited from firing the kilns when alone at the studio. Members must always wear gloves even if they are not pulling pieces - the pulley system used to open the kilns gets very hot.   The use of ferric chloride, a chemical often employed in saggar firing, is prohibited as it is extremely caustic and has, in the past, ruined some of the Pottery Activity's equipment. LMRA may forbid this use of these kilns during extremely dry weather.

raku1
 
raku2
Two of the raku kilns with the propane tank   A barrel kiln, converted electric, and the Brodnax kiln
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Raku glazes
 
 

Raku glazes are low-fire glazes that are specifically formulated to interact with the vagaries of raku firing. In raku firing, pieces are rapidly brought to temperature, then removed while hot from the fire and placed into a container full of flammable material, such as hay, paper or wood shavings. The resulting flame is quickly extinguished with an air-tight seal and the glaze reacts to the loss of oxygen and resultant smoke. Unglazed portions of the pieces will have a black finish.

Crackle raku glazes are intended to craze and form cracks, large or small, in the glaze when the piece comes from the hot fire into the cool air. Waving the piece or blowing on it prior to putting in the reduction bucket will increase crackling. The smoke from the reduction container blackens the crackle and makes it more visible.

Clear crackle glaze can be mixed with mason stains to form a variety of even colors. It can also be applied over oxide stains or low-fire glazes; however, some underglazes applied under clear crackle raku glaze tend to diminish the crackle effect as they can change the expansion and contraction processes of the glaze. Testing will determine which stains and underglazes work best.

Another type of raku glaze relies heavily on reduction for success. These glazes contain different metallic elements which "flash" upon reduction. The secret to these glazes is to move them very quickly from the fire to the reduction container to limit the amount of oxygen in contact with the piece.

Still another type of glaze results in intentionally rough and uneven surfaces, like reptile skin. These glazes are easy to use and do not require rapid transference like metallic glazes. Generally, the thicker these glazes are applied, the more uneven the finish will be.

Other methods of alternative firing in the raku kilns include horsehair and saggar firing. For both of these, pots should be burnished with a stone, spoon or other implement while green. The application of terra sigillata, a thin liquid clay, will ensure a smoother finish.

For horsehair, the bisqued pot is heated to about 1500 degrees in the raku kiln, then removed to a brick. Strands of hair (usually from a horse's tail) are draped across the hot pot and singe black lines into the finish. Feathers can also be used. Grains of sugar dropped on the hot pot make a pleasing design of dots (and smell good too!).

Saggar firing involves enclosing the pot in a container with chemicals and organic material. The container can be a covered pot specifically made for saggar firing, or, more simply, a piece of crumpled tin foil. Chemicals used include sodium (from table or sea salt), magnesium (from Epsom salts) and copper (from Miracle Gro). Strands of copper or steel wool pads can be draped across pots to make colored marks. After firing, the saggared pots will have a swirly, multi-colored finish. Ferric chloride can be sprayed or brushed onto the piece prior to placing in the saggar, but this must be done away from the studio. Members who use ferric chloride typically prepare their pieces at at home, as the use of caustic ferric chloride has been banned at the LMRA Pottery Studio.

Because of the thermal shock inherent in raku firing, some clays are not well-suited to this method. Very smooth clays such as B-mix or low-fire earthenware will crack from thermal shock. White clays work better than red clays, and round forms work better then flat forms, which tend to crack. Some people have had good results with porcelain; others have not. The best bet is to use a white stoneware clay. A very good raku clay specifically formulated for raku firing is available at Texas Pottery Supply in Saganaw, and Trinity Ceramic Supply's white stoneware works well also.

Pieces fired in the raku kiln are not food safe or water tight. They are intended only as decorative pieces.

At the LMRA Pottery Studio, we have six raku glazes, which are in the orange buckets in the glaze room:

  • Clear Crackle
  • Copper Red - green in oxidation, red in reduction, flashes copper
  • Crusty Luster - pale bluish, greenish hues
  • Dragonfly - irridescent reds, greens and blues
  • Alligator - matte green
  • Lubbock Sand - multi-colored with reds and greens, some metallic flashing

Some examples:

 
crackle
 
alligator
Pot with unglazed (black) stripe separating
copper red and clear crackle.
  Alligator
underglaze
 
raku
Clear crackle over low-fire glazes   Copper-Red
copperrattle
crusty dragonfly
lubbock
Copper-Red Crusty Luster Dragonfly Lubbock Sand
horsehair
 
saggar
Horsehair   Saggar
   

What is shrinkage?
 

Wet clay contains a lot of water. Some clay retains more water than others, and some methods, such as throwing, introduces more water into the clay.

As the clay dries, the water evaporates and the piece shrinks. The greatest percentage of shrinkage will occur between the wet and bone dry stages. However, during firing additional shrinkage will occur.

The rate at which a given clay shrinks is important to know. Glaze formulation must take shrinkage into account; if a glaze shrinks more or less than the clay body it covers, it will craze, crawl or pop off of the fired pot. Also, in doing inlays or marbling, multiple types of radically different clay should not be used as the clay bodies may shrink at different rates and cause the mixed clays to separate. For example, if you wanted to make a red and white marbled vase, you should use Trinity red and white stoneware rather than Trinity red and porcelain.

For most of our members, the issue of shrinkage is important in estimating the size of a finished product. Most beginning potters are shocked when their first coffee mug comes out of the glaze fire looking like a demitasse!

The conventional estimates of shrinkage are 6% for low-fire clay, 12% for stoneware, and 14% for porcelain. At the LMRA Pottery Studio, we tested four commonly used clays, fired to both cone 6 and cone 10, to test the conventional wisdom and this is what we found:

 
Clay body
Cone 6 Cone 10
 
Trinity white stoneware
12% 12%
 
Balcones dark
11% 13%
 
Trinity porcelain
11% 13%
 
Speckled Buff
14% 16%
James Freeman, a potter in Michigan, has created a shrinkage rate calculator which runs as an Excel or Open Office spreadsheet. Input the desired finished size of the vessel, the desired wall thickness, and the appropriate clay shrinkage rate, and the calculator tells you not only what size to make the wet vessel, but also the volume of the resulting vessel and the approximate weight of clay required to throw it. Get a copy here.
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Bridget Hauser's stain recipes

Bridget Hauser was a guest instructor at the 2008 LMRA "Four Artist Workshop" and has kindly provided us with the following recipes for stains. She has this to say about them:

"Use with my blessings as stains or decorating engobes.  They work on bisque by themselves or over or under glazes.  Cone 10.  The Black is not food safe when used as a stain on the surface without being sealed with a glaze.  Use as a decorative surface only;  I actually never use the ‘stain only treatment’  on food surfaces.  If it is just stained I keep it to a rim or outside, decorative only. "

 
Black Stain (by grams)
    Black Iron Oxide          250 g
    Cobalt Carbonate         150 g
    Manganese Dioxide     100 g
    Chrome Oxide                50 g
    Gerstley Borate            100 g

Rutile/Iron Stain (by part)
    Base:
    Nepheline Syenite (1 part)
    Gerstley Borate (1 part)
    Tri-Calcium Phosphate (bone ash) (1 part)
    Frit 3110 (1 part)

For Iron: + 8 parts Red Iron Oxide
              + 8 parts Albany Slip (or appropriate substitute)

For Rutile: + 8 parts Rutile Oxide

For Cobalt: + 5 parts Cobalt Carbonate

NOTE: These stains contain chemicals that will make them adhere to kiln shelves and should not be used on the bottoms of pieces.
They are not food safe and should be used only as decoration.
They should not be used for cone 6 firing.

How to apply:
Bridget’s Rutile has a very nice effect if applied by brush and then wiped off with a damp sponge.

Bridget’s Iron can be applied like the Rutile, but is very nice with transparent glaze over. (Just remember that it not to be used on the bottom as you can with the RIO mixed with water.) 

Bridget’s Black has a metal look, and should be applied very thin.

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Glazing tips from Patricia Bridges' blog - bridgespottery.com
  • Allow enough time to glaze. Don't expect to glaze 3 pots in 15 minutes.
  • Unless you are using glazes you have experience with, take time to decide what you like and what would fit the piece. Look at other people's work on the shelves, talk to other members.
  • Think about glazing multiple pieces at a time vs. one here, one there etc.
  • Before you glaze, inspect your pot checking for any burrs or edges that need smoothing. Use one of the sanding tools for a light touch up. It's much easier to do it now than when your pots are fired with glaze.
  • Remove any dust - a damp, clean sponge does the job. If you "wash" the pot, you must allow time for it to fully dry, as glaze will not adhere to the pot very well.
  • The bottom of your piece (where it sits on the kiln shelf) cannot have any glaze or it will stick the kiln shelf and ruin our shelves and your pot. Apply wax resist to areas that will not have glaze. Select a clean brush of an appropriate size and rinse the brush afterwards.
  • Select your glazes carefully. Does it run? Is it matt or glossy, is there a test piece I can look at? Ask an experienced member. Many members know the glazes and want to share their knowledge.
  • Check your glaze to see if it needs better mixing or needs to be thinned. Only glaze committee members can add water to glazes, but you can take a bit out and thin it in another container for your own use. Nothing is worse than dipping a pot only to find out that the glaze has chunks, and it's now all over your pot. Most glazes will have a lump-free, cream- like consistency. If the bucket looks like thick pancake batter, ask for help.
  • Take the time to pour the glaze into a bowl or container that will allow you to glaze your piece easily.
  • You can dip, paint, sponge or spray glaze onto a pot. For dipping , use tongs to dip your pot. Things take longer to dry before you can second dip. Be patient! You will not only ruin your piece if it's still wet before the next dip, but you will contaminate the glaze for others. After you have dipped or painted - WAIT and let it all dry. The glaze will become like a powder finish, and that is when it is safe to touch.
  • Clean the bottoms using a clean sponge, leaving a small band unglazed near the bottom. 1/8th to 1/4 of an inch will create a safe area should your glaze run a bit.
  • Clean up the area, wash your tongs, brushes and bowls.
  • The phrase I hear often is "Oh, I thought I would remember what colors I used..."   Write it down in a notebook - A over B, 2x dip, light dip, painted on etc. Be descriptive about what you did. If you love it , you will want to replicate it.
  • Put your ready-to-be-fired work on the correct shelf in the kiln room.
  • Lastly, leave a note for the kiln loaders if there are any uncertainties or concerns about the piece. If your piece needs to be stilted , leave a note to that effect. If your glaze job looks questionable leave a note and ask an experienced member.

 


Other tips and hints
  • Try to keep thrown pieces of a uniform thickness. Pieces with thin walls and thick bottoms dry unevenly. Sometimes air or water is trapped in the base and though it looks ready to fire, it blows up in the kiln.
  • Throw thick, trim thin. If throwing pieces with thin walls and bases seems impossible, remember that you can trim a lot of clay from your pots when they're leather-hard. Afraid you're going to cut through the base? If that happens, oh, well. It's all a part of learning, and clay can be recycled.
  • Attaching handles. To help ensure handles stay attached, score both the handle and the piece, add slip to both, and press firmly together. A little vinegar also helps it adhere. When pulling or hand-building handles and attaching them to cups or other pieces, often the handle is wetter than the piece it's being attached to. Paint a little wax around the area to keep it from drying unevenly and popping off.
  • Sculptures should be hollow. They should either be formed around an armature, which can be as simple as wads of paper (which burn off in the firing) or hollowed out after the form is finished, by digging out the center from the bottom of the piece or cutting in half, hollowing and reattaching.
  • Hollow items must have air holes. Whether it's a sculpture, rattle, or the base of a goblet, be sure to poke at least one hole in an inconspicuous place to allow air to escape during drying and firing. Make sure the hole is open after you glaze, too.
Here is an example of what happens when a pot is too thick. Several pieces exploded in the kiln and (amazingly) did not damage the kiln or other pots. But the kiln and every coil has to be cleaned when this happens. If you are having trouble getting pieces thin enough, practice by making pots and trimming until you cut through the bottoms and sides. It's harder than you think!
exposion kiln