Terra Sigillata: History

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.

About Decals

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.

Woodgrain finish with stains

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.

Terra sigillata: Application and Firing

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.

Cloth for texture

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.

Troubleshooting: Dull lustres/metallics

Cloudy or dull lustres or metallics may be caused by insufficient ventilation or firing to an excessive temperature.

Description

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

Colour Development

Colour Development
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.

Waterproofing

- 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.

Interesting finish

You can create an interesting finish by mixing a cup of slip with a teaspoon of vinegar and painting it onto greenware.

Thin pieces

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.

using underglazes

When using underglazes, do not backstroke when applying, as this will cause a pile-up of paint or a pulling off of the paint already applied.

drying underglaze

Remember that your colours must be dry before taking any nest step, whether it is firing or adding design work over your underglaze base.

Ceramics Decoration

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!

Terra-Sigillata: Description

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.

Drawing Directly

You can draw directly onto a pot by placing design over carbon paper and tracing the design, you can also sketch right onto the surface with pencil as the lines will burn out in the firing.
hope this has helped!

Application temperature

Pieces to be decorated with overglaze should be at room temperature. Articles from a hot kiln will cause he oils in the overglazes to evaporate

Applying Mother Of Pearl

A proper finish of opal and mother-of-pearl lustre can be guaranteed with a light application.

Antiquing

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.

Attaching pulled handles

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.

Oxide over glaze effortlessly

When applying oxide over dry glaze, the glaze sucks the water out of your brush making it difficult to paint clean lines. Lightly mist the glaze first with water, and the oxide will flow smoothly.

10 Oxide Experiments

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.

Adding extruded handles and attachments

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.

apply raised designs to wet greenware

You can apply raised designs to wet greenware by using a brush syringe or eyedropper filled with slip.

Mixing Oxides

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.)

History

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.

Applying neat lines

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 compared to stains

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.

Stir all colours well

You should stir all colours well before applying except for a few. In setting on the shelf, many colours settle and stirring will help to mix them again.

Applying to a textured body

When applying lustres to a textured surface, be sure to brush out the excess overglaze from the crevices while it is still wet and can be seen. If you do not it will burn off in these recessed areas during firing.

Terra Sigillata: Types

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.

brushing one-strokes

If you plan on using only a small amount of a one-stroke colour, it is possible to obtain the proper painting consistency by loading a wet brush with colour.

Oxide Chart

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.

Troubleshooting: White spots

White spots, or spots of glaze colour showing through your overglaze, are caused by moisture present on the object when the overglaze was applied.

Underglaze design work

Underglazes are poor choices for design work. Since it is necessary to apply three coats for effective coverage, you can see how difficult it would be to make three tines directly on top of each other.

Gold Luster Decals

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.

Over-wetting

If you leave your decal in water too long, too much glue will be removed and it will not fire properly

Slip trailing

There are lots of plastic squeeze bottles on the market today and they can be used in many ways for decorating ceramics. Slip trailing is just one idea.

using underglaze

In most cases three coats are required for using underglaze. Each coat should be applied in opposite directions.

Using one-strokes

One-strokes may be used only under transparent matte glaze.

liquid bright gold

The best known of the overglaze decorations is liquid bright gold which is a true solution of gold in solvents and oils

China Paints

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.

Drying

Pieces that have lustres/overglazes applied to them should be allowed to dry in a area free from contamination by smoke, dust , dirt or moisture before firing.

Applying over glaze

Lustres and metallics take on the surface texture of glazes they are applied over. Satin or matte glazes will yield a dull finish and gloss glaze will yield a dull finish and gloss glaze will yield a shiny finish.

Oil/water base brushes

Never use a brush that has been used to apply a water base product to apply a solvent or oil-based product such as lustre.

apply stains smoothly

It is important to apply stains as smoothly as possible. Any blobs or over-lap lines that are not brushed out during application will show on the finished piece

Stains outdoors

Stains may be used on pieces that are going to be used outdoors. When finished, they should be sprayed with several coats of fixative to prevent moisture from penetrating. It is a good idea to have the inside glazed.

The wonders of Glycerin

A few drops of glycerin (from the Chemist/drugstore) added to engobes, stains, oxides and slips slows drying time and increases workability.

Applying

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.

Thickening china paints

It is possible to thicken china paints with castor oil

What are underglazes

Underglazes as we know them, are opaque. They are formulated from colour pigment and clay to give solid, opaque coverage.

apply one-stroke

You can apply one-stroke with just about anything to a ceramic piece. Brushes, sponges, fingers, etc, will all work

Proper overglaze decorating

Proper overglaze decorating begins with the greenware. Greenware which is to be overglazed should be carefully cleaned and fired to cone 04

Brushes and oil based colours

ince translucent stains are in the oil-base family of colours. You should use brushes for these colours and set them aside strictly for that purpose.
It is necessary to apply some type of sealer to preserve satin work.

storing ware for staining

If you cannot stain your bisque piece immediately after firing, store it in a plastic bag so that household dust and greases do not contaminate the surface.

Cutting intricate patterns?

Cut pieces out of adhesive backed shelf paper and use them for resist. They will stick to greenware and bisque. Using an exacto knife you can cut out lines, shapes, and intricate patterns.

Cloth/slip textures

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.

stamping

Lustre and metallics can be applied by rubber stamping.

Slip description

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.

Coat coverage

Usually one coat coverage of a piece with opaque stains is all that is necessary. You might find, however, that lighter colours require two. If you are trying to cover a darker colour with a lighter shade, you may need several coats.

Making Reds

Reds in glazes and underglazes are the hardest to accomplish and even the most experienced tend to purchase reds as they are so unreliable. Even the bought reds come up a lot better if put over a golden yellow underglaze. My advice is to buy these colours.

A different texture

You know those rolls of rubbery stuff you can buy to cover your shelves to cushion glasses and plates? They make great texture when rolled into slabs.

Mixing

If you get tired of shaking and mixing those jars of paint, try adding a few ‘split shot' sinkers to each jar.

Adding to underglaze

You can change the colour of an opaque underglaze by adding one-stroke to it. You should test fire your new colour before using.

Monochromatic Design

Monochromatic Design
Use a single color for the item(s). A single design may be used, or a combination of designs all in the same color range.
Plan a pleasing design and placement of the decals before application.

Wraps

Wraps
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.

Decals for glass

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.

Adding Oxides

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.

Sealer

You can apply as many coats of sealer to stains as you wish, but you must be sure that each coat is dry before adding another.

When to Apply

Underglazes should be applied to dry greenware. If greenware is still damp when applied, the underglaze colours may chip off after firing.

decorate over a sponged-on froth glaze.

One-strokes can be used to decorate over a sponged-on froth glaze.

Colour ceramic slip

One-strokes can be used to colour ceramic slip. It takes quite a bit but you can do it. You may also add it to slip and swirl it in, casting a piece immediately. When fired, the piece will have a marbled effect.

One-stroke colours

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.

Loading your brush

When loading your brushes in preparation to applying overglaze, do not dip your brush into the overglaze all the way up to the metal ferrule. This only wastes colour and makes brushes hard to clean.

Evaporation

Lustres and metallics do have a suspension agent and are subject to evaporation. This is why there are thinners that can be added to them a drop at a time to get them back to proper painting consistency.

Colour depth

If you want a deeper colour of overglaze, don't try a thick application to do the job. Apply normally and fire, then apply another coat and re-fire.

Brush techniques

Opaque stains are ideal for use in brush techniques. The colours lend themselves to mixing and blending well

Antiquing a piece

Before you antique a piece be sure to apply a good even coverage of a brush-on or spray fixative. This will prevent your translucent from being absorbed and also will help you remove it from unwanted areas more easily.

Terra Sigillata; Description

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.

Repair sealer runs

You can fix Sealer runs. Use the same thinner as you use for cleanup and gently wipe back the run. Be sure to use a cloth that will not leave fiber, as this will stick to the piece.

Appearance

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

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.

Knowing where you have missed.

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.

Texture using underglaze

Since underglazes are largely clay, you can use this as a decorating advantage. Combine some ground clay with the application of your underglaze colours and apply three coats. The piece will have texture.

Multiple applications

You may use more than one overglaze on apiece but they should be fired between applications

Spraying

Lustres can be used in a spray bottle or air-brush. It is necessary to follow cleaning procedures and practice to get the proper coverage.