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Here are 10 ways to experiment with oxides.
1. Brush oxides on greenware, bisque and/or glaze.
2. Make some slip and add some oxides to create colors. To get more uniform colors mix well.
To get more random, blotchy colors don't mix too well.
3. Brush oxide wash over an unfired glaze, then fire. Be very careful when handling as you may smudge the oxide.
4.. Brush oxides on, then apply glaze. Best to dip or spray to avoid brushing the oxide off (and if dipping, best to put some glaze aside so oxide doesn't contaminate your whole batch of glaze.)
Generally the stronger the oxide wash, the more it will bleed through the glaze.
* Both 2 and 3 works well with Opulence glazes, and many of the other glazes. Where specified by the manufacturer this is explained on the label.
5. Mix ball clay with your oxide/water. Is reported to gives a better consistency and tones down the color.
6. Brush a couple different oxides on, overlapping in areas.
7. Sgraffito. Brush on oxide. When dry, scratch with a sharp tool through the oxide to show the clay underneath. Cover with transparent or translucent glaze. Or do the same thing with oxide over unfired glaze.
8. Spatter wax on the surface, and paint the oxide wash over that.
9. Use other masking techniques, such as torn, wet newspaper, and paint an oxide wash over it.
10. Sprinkle a variety of different oxides on a newspaper. Place leather hard objects onto the oxide mixture (for example, a piece of tile). Or use a piece of Styrofoam or a sponge to pick up the oxide and transfer it to your piece. Keep the pattern as it lands, or smear it around. In this bisque and apply glazes; the oxides will still interact with the glazes when fired together.
Cotton lace, burlap, cheesecloth or other cotton, absorbent materials can be soaked in slip and added to pieces for interesting textures. Soak fabric in slip, squeeze out lightly, brush on leatherhard clay surface, dry slowly, and bisque. The fabric will burn out leaving the slip texture behind.
History: Historically terra sigillata has been used as a sealer and decorative coat on pottery for thousands of years. Common examples are the Roman red black pottery, and the black polished Native American Indian pottery of the Southwest. Contemporary uses include raku, smoke firing and other techniques that emphasize the surface.
Decals are available in a huge array of designs and colors, and can be adapted to almost any project with little effort. Technically, decals are overglazes and may be made of china paints, gold, platinum or enamels. They are applied over a fired glaze surface, glass or porcelain bisque, then re-fired. During the firing, glazes soften and most decals sink into the surface and become a permanent part of the item. Metallic decals fuse to the glaze, but remain on top of it, and may wear off as time passes.
- Tung Oil (available in hardware or woodworking stores - Thompson's Water Seal (available in hardware stores, used for sealing wood and concrete) - Acrylic Floor Polish (ie Futura.) (available in the grocery store.) Note that I would not use any of these for dinnerware. Just for vases, flowerpots, etc. And some people use them over glazes just to get a nice subtle shine. And I have been known to use them on the bottom of pots to make them less likely to scratch furniture. Another reason potters want sealers is to protect painted work. For example, people that use acrylic paints on bisque and want to protect the paint. We do sell Duncan spray and brush-on sealers in flat and gloss, which will protect the paint from chipping and smudging, and give it a shine if you wish. They are good for decorative pieces. But these are not waterproof. So if you want your piece to be waterproof, try one of the above products. But since those items work by penetrating the clay, and they probably won't penetrate through the acrylic paint, I would put it on the inside of the piece, then protect the painted outside with an acrylic spray sealer like the Duncan products (or similar items available in the hardware store.) So for example, if you want to waterproof a flowerpot, put the tung oil, Thompson's water seal, or acrylic floor polish on the inside of the pot. Paint and seal the outside.
When glazing a thin piece, glaze the inside, making sure you don't over apply, as the thin walls will absorb a lot of glaze, then wait for it to dry thoroughly before glazing the outside. Otherwise the clay may be saturated and glaze won't absorb and stick to the outside. Some people wait overnight.
A special effect of woodgrain can be accomplished easily. Simply cover the entire piece with your choice of colour and wipe piece down with a wrinkled piece of newspaper. Be sure to do your wiping in one direction. The newspaper will absorb some colour leaviing woodgrain streaks where the colour remains.
Any type of cotton or cloth will burn out during the firing process. For a different effect, you can try soaking cloth or cotton in slip and adding it to your piece for decoration. During the firing process it will fire out leaving just the thin layer of clay that it originally absorbed. Most people think that this only applies to porcelain, but it can be used with ceramic slips as well.
Keep in mind, Oxides are strong colorants, so a little bit goes a long way. In a solution you will probably only want about 2-8% or you will end up with black. Use a respirator or mask when handling the dry oxides.
Remember that using oxides like this will provide unpredictable, but sometimes beautiful results. Test! And Take Notes! (I had to throw that in because I am lousy at taking notes, but getting better. It definitely helps.)
Application and Firing: Terra sigillata can be applied by spraying, dipping or brushing at all stages of construction. Apply several coats and burnish or simply polish with your hands or a soft cloth when damp/dry to the touch. Polish between coats for the glossiest surfaces. Terra sigillata can be fired at any temperature but the polished surface will start to break down when fired over cone 04. Use as a slip/engobe up to cone 10 and above.
How does oxide compare to stain? An oxide is a raw material. A stain is a commercial blend of raw materials (including oxides) to achieve an accurate, consistent color. Glazes and slips made with stain will generally be more uniform, whereas those made with oxide will be more splotchy, speckly, and variable (in other words, beautiful!). There are 4 main colorants used. Sometimes you will see them as oxides, sometimes as carbonates. For example, cobalt oxide and cobalt carbonate. The oxides are generally stronger in color and coarser grained (more speckly.) The carbonates are generally finer grained.
Cloudy looking decals or decals where the colour is not bright need to be burned out and carbon monoxide fumes have to be removed from the kiln. Manual venting by propping the lid and removal of peephole plugs will improve the firing, but may not help bring enough air to the bottom of the kiln or to distribute it evenly throughout the load. A downdraft vent system will ensure sufficient air is brought into the kiln and circulated throughout.
When antiquing, only remove colour from raised areas of a piece, leaving colour in crevices to accent the detail.
If you wipe off too much colour when wiping off translucent stains, you can re-apply and start the process all over again.
The amount of translucent stain you leave on a piece will determine the lightness or darkness of your entire finished piece.
Have you ever tried fluting a piece (carving straight lines into the sides), only to find your lines are crooked or uneven? Make a triangle out of a piece of cardboard, or use a plastic triangle used for geometry (buy in an office supply store or drugstore). Hold the bottom of the triangle against the work surface. For straight lines, brace your carving tool against the straight edge. For angled lines, run your carving tool along the angled edge. This will make sure the lines are all at the same angle.
Oxides can be added to clay (mix with water then knead in), but this is expensive for deep coloring of large pieces. They can be added to slip or glazes. At stoneware temperatures, they can also or used on their own. Mix with water (mix often as it settles fast), brush on bisque, fire.
This is a way to get colored but still “natural” looking surfaces.
Engobes can be defined as liquid clay slips of varying compositions which are applied to the surface of a clay object, e.g. a pot. The purpose of the engobe can be as different as the varied forms it comes in: to give color to a piece; to improve the surface texture; to provide a ground to do further decoration on; to add textures.
Engobes can be applied to wet clay surfaces, leather-hard ware, greenware and even bisqued wares. In each case the engobe's shrinkage rate should match that of the clay underneath, otherwise cracking (when the engobe shrinks more than the clay underneath) or shivering (when the clay underneath shrinks more than the engobe on top) can occur. While there are some basic engobe recipes around, The Potter's Complete Book of Clay and Glazes by James Chappel has a range of engobe recipes for diferent grades of moisture content and firing ranges from cone 10 up to cone 11
Terra-Sigillata is a slip, made of clays whose particles are extremely fine. Like slip or en-globe - which it basically is - Terra-Sigillata appeals to those who wish to develop an intimate relationship between the surface of their work and its form, and who respond to the way in which the Terra-Sigillata becomes an integral part of the clay body rather than coating the surface like a glaze. After the final firing the forms are hand-polished with Tung Oil to achieve a more durable surface. Terra-Sigillata means "sealed earth". It was used by the Greeks and Romans before the invention of glaze.
Terra Sigillata (or earth seal) is a slip containing very fine particles. It is created by a process of separation. We grind, using a ball mill, specially selected clays and water until the particles are extremely small. Deflocculant is added and the mixture is allowed to settle for twenty-four to forty-eight hours. The fluid left on top after settling is terra sigillata. Longer settling will yield a finer, higher quality product. After application, simple polishing with your hands or a soft cloth will shine terra sigillata to a high gloss. This smooth surface is ideal for decoration especially with smoke firing and other primitive techniques. After firing you will have a smooth, weather resistant coating much like a glaze.
History of Maiolica
Maiolica is an Italian earthenware with an opaque white glaze containing tin-oxide. Its most outstanding feature is its splendidly colorful decoration which, unlike paintings or tapestries, remains unfaded over time. Its introduction in Italy long preceded the use of the word "Maiolica" which was derived from Majorca in Spain, where ships carrying lusterware from Valencia stopped on their way to Italy. The tin-glaze technique originated in Mesopotamia (modern Iraq) during the ninth century, almost certainly in an effort to emulate white stoneware and early porcelains imported from China. It was soon found to provide an excellent surface for colored decoration and the technique spread through the Islamic middle east and was taken to Africa, Southern Spain and Sicily when the Arabs conquered those areas.
Maiolica seems to have been established in Italy around 1200 but how it was introduced is not entirely clear. Some believe that the popularity of tin-glazed wares imported from the Middle East led to imitation while others believe the technique was introduced through the immigration of Arab potters to Italy from Spain or Sicily.
Maiolica is usually associated with the Renaissance when its aesthetic quality was at its peak. Improvements in kilns and glazes, and the introduction of new colors which could withstand high firing temperatures made possible the development of more sophisticated decorative patterns.
If you haven't decorated with slips, you're missing out. One of the benefits is that the slips stay put, so designs don't blur or run, unlike many glazes. This also means you can make textures in the slip that will stay exactly as you made them. And you can make designs that won't work with glazes since glazes need multiple coats (ie splattering.) You can squeeze slip out of a bottle into designs (slip trailing) and use it for sgraffito (coat with slip then scratch designs in the slip exposing the raw clay.) (Note: sometimes decorating slips are called engobes, and the terminology isn't tightly defined; they are generally the same thing.) Slips are best applied to leatherhard greenware, but may be used on bisque also. They may be used on low-fire and high-fire clay. The slip must be similar to the clay however, so the shrinkage between the two is similar and the slip doesn't crack or peel off.
Once you have the piece you want and have completed the necessary processing, you are ready for ceramics decoration. There are so many styles to choose from that you may want to start simple and develop your own unique style after some experience. Glazes run the gamut from the simple to the sublime using chemicals, metals and other compounds to achieve incredible results. The most important part of ceramics decoration - have fun!
Since one-strokes are pure colour pigment, the colour you see in the jar is the colour you will obtain on a finished piece.
It is possible to mix two one-stroke colours to make a third. Since they are pure colour, you will know immediately if the mixture is the way you want it to be.
Attaching pulled handles: Once all handles are pulled and firmed, (approx.1/2 hr), they are ready to attach. I will describe this process as connecting to a mug, though it is the same procedure no matter the form. 1. Take handle and flatten the large end with a flat piece of wood ie ruler, wooden spoon back. 2. With a fork or other tool cross hatch both the flattened end of the handle and the point on the pot you wish to attach the handle, with an old toothbrush, wet these areas with water or slip. 3. Attach the hatched end to the pot and press and wiggle it gently until you feel adhesion 4. Pick up the pot and hold arm extended as when pulling the handle, and continue pulling in the same way until desired thickness, squeeze off any excess clay and join other end to pot by pushing into place. 5. Leave upside down to dry. Note: Handles dry faster than ware, so keep them covered with plastic or put on ware board with all handles facing inward.
If overglazes are applied to a textured surface and they fire off the raised areas, but fire perfectly in the recessed areas, this usually indicates an over-application of colour. The weight of the material applied pulled its off and onto the recessed areas.
Types of Terra Sigillata: The basic mix is a white ball clay. Used alone it is a beautiful satiny white. Mason stains and other colorants can be added to give a wide range of colors. Use between 3 and 10%. To eliminate weighing use 1/2 or 1 full standard Mason sample pack per pint of terra sigillata. White, red and tan slips can be intermixed to yield different tones.
Gold Luster Decals
These decals may be applied to clear or colored glazes. They may also be added on top of a fired decal and re-fired for a layered effect. Applying gold decals on a dark glaze surface can be tricky because the dark brown coloring of the gold decal may blend in with the dark glaze color. Try to be as accurate as possible with the decal placement. Touches of liquid fired gold trim or lettering can be added after the gold decal has dried. Clean these areas with denatured alcohol to remove all traces of adhesive from the decal before applying the liquid gold.
China paints belong to the overglaze family of colours.
If an area to be covered with china paints is large enough or does not have too many recessed areas, you may have better luck in applying colours with a pad.
A pad , as referred to in china painting, is a piece of china silk filled with either cotton or lamb's wool and tied together to form a loose ball.
You can create a marble effect using your translucent stains. Simply pour a bit of several contrasting colours into a container of water large enough to emmerse your bisque piece. Stir the water with stain on top of it slightly and immediately dip your bisque piece into it. The colour will adhere to the bisque leaving a marbled appearance. Be sure to hold piece in a non-vital area and do the dipping quickly. You can spray fix after it''s dry.
Place one decal at a time in warm water in a container large enough to allow the decal to be flat. A decal will curl up in the water. In about 15 seconds, check to see if the decal has started to release from the backing paper. If not, allow it to soak until it does start to release, but do not allow the decal to slide off the backing paper into the water. Remove the decal from the water and place it on paper toweling until it flattens again. Make sure the area where the decal will be applied has been cleaned with a damp paper towel. With the backing paper still attached, place the decal into position, face up. Hold the decal in place and gently slide out the backing paper. Use a decal squeegee to gently work out air bubbles from under the decal. Always work from the center toward the edges. Allow the item to dry for 24 hours, then fire it to the recommended temperature. This is usually cone 015-016 for china paint or metallic decals, and cone 022 for glass decals.
Adding extruded handles and attachments: These are the easiest handles and lugs to make, though making them look a part of the pot is quite a challenge, but can be achieved with practice. 1. Crosshatch and slip joins and pot at locations of adhesion. 2. Press handle on firmly, wiggling until adhesion is felt. 3. Sponge to clean.
You may not know it but you can accomplish a variety of techniques in the lace draping field by using opaque stains mixed with white glue. Simply mix the two together, soak lace in the mixture and add to an already stained piece, such as a doll for decoration the lace will dry hard and you will have the colour you want
Using a glass or clear container, dissolve 5 gms of calgon sodium hexametaphosphate, which is a deflocculating agent) in 2 pints of rainwater(sodium crbonate or potassium carbonate can also be used). Add 230 gof dry crushed clay, sieve through a 60 mesh (or finer). Shake container, mix and leave for three days minimum. The clay will settle into 3 layers with a layer of clear water on top, siphon off this clear water and discard. The next layer is the terrasigillata(colloidal slip).
Note: White clay needs 0.3% sodium silicate......and water to clay ratio of four to one, to deflocculate.
Red clay needs 0.5% sodium silicate......and water to clay ratio of three to one to deflocculate. Terra sigillata is high in alumina. It may be hardened by adding 3-4% sodium silicate to the recipe after deflocculating the sigillata.
The following chart can be used as a guide for adding percentages of oxides to engobe recipes for color results. These colors refer to results obtained in oxidatiion firings:
Cobalt Oxide Dark Blue 1.5
Copper Oxide Mid Green 3.0
Yellow Ochre Ochre 4.5
Iron Oxide Mid Tan 3.0
Rutile Creamy Tan 6.0
Iron Chromate Dark Gray 3.0
Manganese Dioxide Purple Brown 6.0
Fire in Oxidation for the above color results.
A decal isn't fired that much differently than any other piece of ware, although there are some special considerations. Venting is very important to good results with decals - especially to get true colours.
Problems related to venting include: poor colour development, a cloudy or hazy appearance. Proper heatwork is also an important factor. Decals that are under or overfired may exibit the following: faded colours (overfired), colour shift (underfired), decals rub off (underfired), dull appearing metallics (underfired)
A favourite technique for the use of underglazes is sgrafitto. Apply your normal three coats and let dry. Transfer a pattern to piece and, with a sharp tool, scribe or cut through the underglaze into the greenware. You should slightly dampen lines you are scribing to prevent chipping. When completed, fire as normal, then add covering glaze and fire again. Scribed lines will show white through your underglaze covering.
Trim the decal to fit the item. Mug wraps are normally about seven to eight inches in length and 2¾ to 3½ inches high.
After soaking the decal, hold it by one end and gently pull out the backing paper as you rotate the item. Position the wrap evenly around the mug before using the squeegee to press out air bubbles.
Decal Firing Tips
Decals offer an opportunity to add decoration to ceramic and glass ware without the time and skill required for hand painting. When properly applied and fired, decals can add colour, texture, design and personalization to a piece. To achieve professional results with decals, it's important to understand how to select, apply and fire the decals.
One-fire Decal Layering
Before applying the decal, trim excess clear background from around lettering or numbers. Place lettering and/or numbers on first. Make sure they adhere well and dry for approximately six hours before applying the second layer. For this project, the second layer is a pastel floral design. Apply the second decal, allow it to dry, and fire the pieces.
Decals are similar to a sandwich. There's backing paper on the bottom, the actual design colors in the middle, and a protective film coating on top that burns away during firing. There may also be a piece of wax paper over the decal to protect it during shipping and handling. It's important to keep decals at a constant moderate temperature, a constant humidity, and stored in small piles, not high stacks or bunches.
Measuring Heat Distribution
Differences in heat distribution from top to bottom in the kiln are usually far more noticeable for cooler firings like decals. A 2 or 3 cone difference at 022 may only be a 1 cone difference at cone 6. This is because at higher temperatures radiation heats the kiln more effectively. Slowing the first half of the firing can help heat distribution problems. This also helps by allowing more time for air to enter the kiln and burn out organics and for carbon monoxide to leave the kiln. Use a controller to set heating rates and soaks for more precise firings.
Mural designs are available in a wide range of sizes. They can be adapted to serving trays, wall hangings, message boards or back splashes. Place tiles on a flat surface and brace all edges so the tiles do not move. Apply the decal, remove all air bubbles, and use a sharp razor blade to cut the decal where the tiles meet. After firing, adhere the tiles to a tray, frame or wall. Grout the tiles if necessary.
Copper Carbonate and Copper Oxide. (Note: Copper should not be used in soluble glazes for food and drink containers; in addition to not being safe, it will leach into tea for example, making your tea have a coppery taste.) Not very effective used on it's own. Better to add to or cover with glaze. In an electric kiln it will create a variety of green shades.
In alkaline glazes it will create turquoises. It may achieve red colors in a reduction kiln.
If you experience difficulty in seeing what areas of your bisque you have or have not covered with white opaque stain, you can dampen your piece lightly with a sponge and those areas that you have missed will show up and through, usually a little on the yellowish side.
To make an add-on, all you have to do is select a flat mold or plaster bat and pour the slip on the flat surface. To make an add –on, work the wet clay in your hands like bread dough, folding from time to time to eliminate air bubbles. A few drops of glycerine or warm water will slow the drying time of a piece of clay you are working with your hands to form an add-on. To attach an add-on to a piece of greenware, use liquid clay or slip. It is best to dampen the greenware surface before applying the add-on. Be sure to apply your add-on solidly to the greenware. Any air pockets left under your add-on will make for and explosion in the kiln later.
One-strokes are concentrated colour pigments with no clay added and may be translucent or opaque.
Soluable in water, one-strokes can be used for washes, outlines and small areas of concentrated colour.
One-strokes are not recommended for large area coverage. These are concentrated colours and will streak if not applied properly.
As the name implies, only one coat of colour is needed when using one-strokes.
Metallic paste is a combination of metallic particles suspended in thick paste to help in the application.
Metallic pastes are generally used to accent detail and are generally and oil base product.
Metallic pastes are most commonly applied over another opaque colour with a soft rag or finger tip.
Although often forgotten, it is best to seal paste metallics onto pieces with a coating of spray or brush-on fixative.
The colour in the jar of underglaze is not the resulting colour when fired. You can change the colour of underglazes with the addition of one-strokes (pure colour pigments) in varying quantities. Since you still will not be able to tell the colour you have made until after the piece is fired, it is recommended to make a test-firing of piece to be sure the colour is what you want.
An overglaze marbleizer is a special effect product that is used with other metallic and lustre overglazes. It is applied over other products and when fired produces a star burst, spider web effect.
You cannot apply marbleizer to an overglazed piece until the other overglazes are completely dry.
Various oxides, carbonates and commercial stains can be used to color base engobe recipes. If you want to use commercial stains, refer to your manufacturer or sales outlet for more information on what percentages to use, or experiment yourself with your own line blend.
These underglaze crayons can be used to draw on greenware or bisqueware. The work can then be glaze-fired normally.
Difficulty Level: easy Time Required: 120 min
Ingredients: White Firing Ball Clay (50%) Potash Feldspar (25%) Flint (Quartz) (25%) Bentonite (5%) Colorant (15%) (Iron Oxide, Copper Carbonate, Cobalt Oxide/Cobalt Carbonate or any undeglaze colorant).
Mix the ingredients with the desired colors and dry sieve the powder through an 80 mesh.
Weigh the ingredients and then measure out 45% of that weight in water.
For every 100 gm (4 ounces) of powder, mix in a teaspoon of sodium silicate to the water.
Add the water to the powder and mix thoroughly with a fork or similar tool.
Roll into a pencil shapes.
After drying, fire the pencils/crayons to 800o - 900o C.
Be sure to wear a mask and gloves, if using toxic colorants.
Experiment with different color percentages.
Try out making pencils of different sizes, for different drawing requirements.
Ceramic Toxic Materials
Thanks to Steven Goldate: http://www.ceramicstoday.com
Any problems incurred when working with decals are usually due to poor application technique. Remember the following:
• Always wipe the item down with a damp cloth
• Use clean, warm water to soak decals
• Squeegee the item well to remove all air bubbles and to ensure good adhesion
• Dry the item 24 hours before firing
Although rare, firing problems can usually be solved by re-firing the item one cone hotter and making sure there is adequate air circulation within the kiln.
Bad decals are extremely rare. They may have been contaminated during the printing process, there may be a compatibility problem between the decal and the glaze, or the covercoat may be too heavy or too thin.
Cobalt Carbonate and Cobalt Oxide. This is the most powerful color and produces various shades of blue. It can be harsh used by itself, so is sometimes mixed with iron, manganese, magnesium or copper to create more subtle colors. Like iron oxide, it can be added to glaze, or can be applied to the clay surface and fired to stoneware temperatures. By itself it will tend to create a dark slate metallic finish.
It can be mixed with manganese and iron to produce rich black slips.
THE RENAISSANCE TECHNIQUE
The basic raw material, red clay or chalky clay, was dug from river beds or pits, impurities were removed and the clay was well kneaded to remove any air pockets within the clay before it was thrown on the potter's wheel or pressed over or into plaster moulds to form vessels. The first firing took place at about 1,000 degrees centigrade in a wood burning kiln. After removal, the pots, now either a pale reddish brown (terra cotta) or cream in color were ready for glazing.
The making of the tin glaze or 'bianco' (white) was a complex process. First, white sand and potash (potassium carbonate especially in its crude impure form obtained from wood ashes) in the form of calcined wine lees (from the inside of barrels) were heated in a pot until they fused into a glassy lump. This was then finely ground and suspended in water with oxides of lead and tin, the last rendering the glaze white and opaque. This sloppy liquid was then applied to the pots, and after a short period of drying time they were ready for painting. The pigments of the color when brushed on the glaze sink into the glaze. Decorators had to be extremely deft because once a mistake was made it could not be corrected. Their pigments were based on metal oxides: cobalt for blue; copper for green; antimony for yellow; manganese for purplish-brown; tin for white. Red was obtained by fluxing Armenian bole with lead, but it was difficult to fire successfully and therefore occurs infrequently on renaissance Maiolica. The pots were then fired again at 950 degrees centigrade.
When using one-strokes you may find that colours look too light after your piece has been fired. This is caused by not applying enough coulour. If you apply too much however, there is a possibility of it popping off.
Do not apply one-stroke by flowing it on like glaze. Simply load your brush properly and apply it in smooth, even strokes.
All brush streaks will show when applying one-stroke. Even, smooth coverage is important.
Measuring Heatwork: Heatwork is another critical factor in the colour development of decals. Fading, Shifting and dullness are signs of too much or tool little heatwork. This is also true when decals rub off after firing. (White or blank spots or burned off areas are generally related to application, not firing.) Use witness cones to measure heatwork and to check the heat distribution in the kiln. Firing to a temperature or firing to a Kiln-Sitter cone may not give the same results as found with a witness cone next to the ware.
One-strokes that have curled or peeled away from the surface painted over a matte glaze are caused by too heavy an application of colour.
Streaked or running strokes painted with one-strokes may be caused by attempts to glaze over one-strokes before firing.
If one-strokes are too dark after being fired, you may be applying too much colour.
If you are having trouble removing translucent stains from your brushes, try using ordinary lemon oil furniture polish. Slightly dip brush and wipe out well. Oil will help condition the brush. Since transulcents are oil based, you only use this brush for oil base colours.
Determining Firing Range
Because the colours on decals can so easily be affected by the amount of heatwork they receive, we recommend test firings to determine the best firing range.
Use a series of witness cones to fire samples of the decals on tiles or blanks. Make several firings and then select the fired appearance which looks the best.
Mixing: Note that recipes typically add up to 100g. If you multiply all the ingredients in the above recipes by 10, you will get 1000 grams, which will fill about 1/2 of a 5 gallon bucket. You can then divide this up into 5 1 gallon buckets and mix different stains in each. As a starting point, use about 15% of the total grams of stain. (eg 1000 grams / 5 = 200 grams per color, 15% of 200g is 30g, so use 30g of each stain)
The classic method is to pre-mix the dry ingredients, then add them to water. But many experienced potters do not premix their dry ingredients. They simply drop them into the water and mix with a jiffy mixer or paint mixer attached to a power drill. Use about half the volume of the dry ingredients for the amount of water. Mix the ingredients into the water with your hand or a stick before using the drill, to avoid stirring up dust. Depending on how well your mixer does, if the slip is lumpy you will want to push it through a sieve.
The completed slip should be the thickness of cream for greenware, or slightly thinner on bisque. Apply slip with a brush, a slip-trailing bottle, or by dipping. As you work, your piece will dry out, so spritz with water periodically, and wrap tightly between sessions. You can build up multiple layers of slip to make very intricate designs.
To make application of non firing metallics(brush on or spray) even, apply a coat of opaque stain over the bisque and under your metallics. Since you are covering up the colour used with a metallic you can use up bits of colour you hve in old jars, even several colours if you wish.
Manganese Dioxide and Manganese Carbonate. In glazes creates colors such as mauve, purple and brown depending on the other ingredients present. By itself it produces an attractive brown with tiny metallic specks at stoneware temperatures (dioxide is specklier than carbonate).
It is often mixed with other oxides such as cobalt to create purples and iron to produce rich browns.
Application techniques for engobes also greatly vary. They range from dipping to brushing and spraying and even slip-trailing, However, in contrast to applying glazes to bisque ware, it pays to be careful when applying engobes to greenware, as the clay can soften and deform, e.g. if a pot is dipped too long. During application, wax or latex can be applied as a resist. Once the engobe has hardened, designs can be scratched in, revealing the clay body underneath.
Iron Oxide. This comes in many varieties and can provide a wide variety of colors under different firing conditions. Types of iron oxide are red iron oxide, black iron oxide, and yellow ochre. At earthenware temperatures, up to 4 percent oxide will produce amber and honey glazes.
At stoneware temperatures it can be applied directly to stain the clay surface. It is often used in this way to highlight textured surfaces. Can also be added to glazes.
To apply decals, first be sure a glazed surface will accept them. Always check the label of a glaze to make sure it reads overglaze compatible. Next, choose a glaze colour that will enhance your decal. Since most decals are china paints, their colours are translucent. So, a clear or lightly coloured glaze is the best choice. However, enamel decals are opaque and look best on dark glaze colours. Metallic decals adapt to a number of glaze finishes. Decals will also take on the finish of a glaze, so the same decal applied to a gloss glaze will appear different on a matte glaze.
How to do Easy Relief Surfaces
Flowers, abstract geometry, letters, anything -- making complex relief surfaces on your pots, tiles or sculptures is easy using shellac. This technique is especially suited to fine clays like porcelain or porcelaineous stoneware, but could be used on just about any clay.
Dissolve shellac flakes to a thin, creamy consistency in Methylated Spirits (Alcohol).
Paint your designs with various brush sizes on to bone dry greenware.
If necessary apply a couple of coats. This will depend on the initial consistency of the shellac.
Let the shellac dry thoroughly. If you're in a hurry, you can use a hair dryer set to 'hot'.
Carefully wipe back layers of clay with a wet sponge. The clay will stay raised where you have applied the shellac.
After drying, the process may be repeated for layers of various depths.
Decorate, glaze and fire as usual.
Be careful not to use too much water at any one time, otherwise cracks may appear, especially on thin ware.
Further effects can be achieved by additional carving.
Try experimenting with other nontraditional resist materials, like house paint!
Translucent stains are primarily used to accent the detail of a piece and may be either water or oil base.
Translucent stains can be used for a rouging technique when only a small bit of colour is added to certain areas with a soft rag wrapped around your finger.
Stains can be used directly on bisque rather than over sealed opaque stains, but they do soak in rapidly and are very hard to control. Translucent colours are very difficult if not impossible to remove from clothing.
Different decals are made for glass and ceramics. Ceramic decals often fire hotter than those for glass. application: decals must have good contact with the surface of the ware, all wrinkles and bubbles need to be smoothed away. Avoid tearing the decal. Firing: decals are generally low firing - cone 022 to 016, check the package for the proper firing range. Venting: Decals contain lots of organics which need to be burned off. Often smelly fumes result during decal firings.
Here is a recipe that is often used because it fits a wide variety of low fire clay bodies. Thinned, it works well on bisque also.
Kentucky Ball Clay (Old Mine #4) 40g
EPK (Kaolin, sometimes called China Clay) 20g
Nepheline Syenite (flux) 10g
Silica Sand (sometimes called Flint) 15g
|Jennifer Mathes, Ph.D.|