Slip and underglaze are both materials used in ceramics, but serve different purposes. Slip is a liquid mixture of clay and water used for forming ceramic pieces and as a base for glaze. Underglaze, on the other hand, is a colored material applied to the bisque-fired clay before the final glaze firing. It creates a permanent color that can’t be changed after glazing and firing.
Understanding Slip and Underglaze
What Is Slip?
Slip Casting
Clay and water are combined in slip to create pottery in ceramics. It forms a thin layer that dries and hardens to form a solid surface when it is poured or brushed onto a mold or piece of pottery. When liquid slip is put into a plaster mold and allowed to cure, it creates a replica of the mold that may be further shaped into the desired shape. This process is known as slip casting.
A common technique for creating precise and repeatable ceramic forms, particularly for bigger or more complex structures, is slip casting.
- The completed ceramic piece’s desired shape is translated into a plaster mold.
- Create the “slip” by combining clay and water to create a liquid.
- The mold is filled to the correct level after the slip has been properly poured into it.
- Wait for the slip to set in order to assist reduce the quantity of air trapped in the mold. The slip is given time to settle and somewhat thicken.
- Remove the extra slip carefully from the mold, leaving a thin layer of clay that adheres to the interior of the mold.
- Dry the slip: After the slip-filled mold has dried, the clay contracts and pops out of the plaster mold.
- In order to extract the cast piece from the mold once it has dried, the mold is often lightly tapped or flexed.
- When the cast object is bisque fired, the clay is set and made sufficiently sturdy to handle.
- After the cast object has been given the required finish and is ready for use, it can be glazed and glaze fired.
Slip casting is an effective method for creating exact and repeatable forms, it is also somewhat time-consuming and necessitates a high-quality mold.
Forming Ceramic Pieces Using Slip
In addition to smoothing surfaces and filling fractures, slip can be used to bind two pieces of clay together. For ceramic artists and potters, slip is a crucial tool since it enables more accuracy and efficiency in the creation of pottery.
The steps below are necessary to bind two pieces of clay together using slip:
- To make the slip, combine clay and water in a smooth combination.
- Clean the surfaces of the two clay pieces that will be linked, and make sure they securely fit one another.
- Make sure the slip completely fills the gaps by applying it to the seam between the two parts.
- To create a uniform and flawless bond, smooth the slip’s surface with a tool or your finger.
- Allow the linked pieces to dry completely, usually over the course of an overnight or longer period of time depending on the slip’s thickness.
- After the surface has dried, use a sharp tool to trim any extra slip and touchup as needed.
- After the parts are linked, they are bisque fired, which hardens the slip and cements the connection.
The finished clay object is stronger and smoother when clay is joined together with slip as opposed to when clay is merely pushed or squeezed together.
What Is An Underglaze
Before the clay is fired, a type of ceramic glaze called an underglaze is applied to give the surface a beautiful aspect. Underglazes, in contrast to other glazes, are fused with the clay body rather than melting into a smooth, glassy finish upon firing. Underglazes are available in a variety of hues and can be used to print, paint, or draw pictures on clay. To add color to the finished product and safeguard the design against deterioration, they are frequently used in combination with a transparent glaze.
The following steps are involved in decorating with an underglaze:
- To allow the underglaze to absorb into the clay body, the clay piece must be clean, dry, and porous.
- Several methods, including brushing, pouring, and printing, can be used to apply the Underglaze. To get the underglaze to the right consistency, you can thin it out with water.
- Before handling the work, let the underglaze completely dry. Depending on the temperature and humidity, this can take a few hours or perhaps a whole night.
- The piece is prepared for firing once the underglaze has cured. The work needs to be fired at a temperature appropriate for the underglaze and clay types utilized.
- To protect the underglaze design and add gloss to the finished item, a clear glaze can be used after firing.
- The item is then fired a final time at a higher temperature, melting the clear glaze to the surface and giving it a glossy, smooth finish.
The Origins Of Slip And Underglaze Pottery
Ancient cultures, particularly those of China and the Middle East, are where slip and underglaze pottery first appeared.
In ancient China, slip casting was initially utilized during the Han Dynasty (206 BC – 220 AD). Ornate teapots, vases, and figurines, as well as other delicate and elaborate shapes, were produced using it. Slip, a liquid form of clay, is poured into a mold during the procedure, and once it has dried, the mold is removed to show the cast shape.
Ancient China also employed underglaze decoration, which peaked in popularity during the Tang and Song dynasties (618-1279 AD). In order to create a vivid, long-lasting design that was resistant to wear and fading, a pigmented underglaze was applied to a clay object before the final firing.
Both slip casting and underglaze ornamentation have undergone several modifications and developments throughout history and are still utilized in contemporary ceramic arts and industry.
What Are The Different Types Of Slip And Underglaze Pottery?
Three basic categories—earthenware, stoneware, and porcelain—can be used to classify slip and underglaze pottery.
Earthenware
Earthenware is a form of clay that is porous, often fired at lower temperatures (about 1,000°C), and has a low fired strength. It is frequently adorned with underglaze colors and coated with a clear or colored slip.
Stoneware
A particular kind of clay called stoneware is fired at greater temperatures (about 1,200°C) to create a denser and harder product. It can be ornamented with underglaze colors or a combination of underglaze and glaze, and is frequently coated with a thick, opaque glaze.
Porcelain
Clay is used to make porcelain, which is fired at temperatures as high as 1,400°C to create a material that is dense, hard, and translucent. Porcelain can be painted with underglaze colors or applied decals and is normally coated with a smooth, glossy surface.
Brush Glazing Is A Method Of Applying Glaze
Applying glaze to ceramics by brushing it onto the surface is known as brush glazing. When fired in a kiln, the glaze, which is often a liquid mixture of elements like clay, feldspar, and other minerals, will fuse and harden.
In order to brush glaze pottery:
- The clay object you intend to glaze should be cleaned and dried.
- Mix the glaze to the appropriate consistency before using.
- Apply the glaze on the pottery with the brush, being careful not to leave any thick spots or drips.
- Prior to kiln firing, allow the glaze to completely dry.
- There are several different ways to glaze pottery, including dipping, pouring, and spray glazing, therefore not all potters use brush glazing. Some potters prefer brush glazing because it enables them to carefully regulate the glaze’s thickness and apply it to specific locations. Additionally, brush glazing gives the potter more creative freedom because it enables them to apply the glaze in a variety of textures and patterns.
When glazing with a brush, you can regulate the thickness of the glaze and apply it evenly, which can assist assure consistent results and a more finished appearance. Additionally, the potter can experiment with different brush strokes, patterns, and other aspects of the glazing process to produce distinctive outcomes, which promotes greater creativity and artistic expression. Additionally, brush glazing is an easy and inexpensive way to glaze pottery, making it available to potters of all skill levels and financial circumstances.
Brush Selection Is Key When Applying Glaze
The choice of brush is important for brush glazing. The final outcome can be highly influenced by the brush you choose because it has an effect on how the glaze flows and is applied to the pottery. The bristles, shapes, and sizes of various brushes can result in a variety of effects.
For instance, a round brush can be used to produce a more textured look while a flat brush can be used to apply a glaze layer that is level and smooth. A liner brush can be used to draw exact lines and details, whilst a fan brush can be used to draw sweeping, softer lines.
It’s crucial to select a brush that matches the glaze you’re using, the size, and the shape of the ceramic piece you’re glazing. Applying the glaze evenly or getting to particular regions of the pottery may be challenging with a brush that is too small or too large.
I recommend to start with a simple brush set and try out various varieties to determine which suits you and your unique glazing demands the most. Many potters choose high-quality brushes composed of natural fibers, such sable or hog bristle, since they offer good control and a smooth application.
Glazing Preparation
When it comes to glazing pottery, preparation is crucial. When the pottery is properly prepared, the glaze will adhere well, produce a smooth and even surface, and help prevent frequent issues like bubbles or drips.
When getting ready for glazing:
- Thoroughly clean the pottery before glazing it to get rid of any dirt or other impurities that can interfere with the glaze’s application. Cleaning the surface delicately can be accomplished with a soft brush, sponge, or cloth.
- Before glazing, the pottery must totally dry out since any moisture on the surface can interfere with the glaze’s ability to adhere. Depending on the size and shape of the pottery, drying timeframes can vary, but it’s often ideal to let it cure for at least 24 hours.
- Preparing the glaze involves combining a glaze powder with water to the correct consistency. Glaze recipes can vary greatly. To make sure that all of the components are dispersed evenly, it is crucial to properly follow the directions and thoroughly mix the glaze.
- To make sure the glaze is the proper consistency and color before putting it to the pottery, test it on a tiny, discrete piece. You can avoid any unforeseen circumstances or issues by doing this.
- Because glazing can be messy, it’s crucial to create a location that is tidy, well-lit, and convenient. It is best to use a table or countertop that can fit your ceramics. To shield it from drips and spills, you might also wish to cover your workspace with plastic or newspaper.
Mixing The Glaze Correctly
The glazing procedure requires careful glaze mixing because the outcome depends heavily on it. The following advice will help you properly mix your glaze.
- Glaze recipes can vary greatly, so it’s crucial to pay close attention to the directions to make sure you’re using the right components in the appropriate quantities. To achieve consistent results, be careful to measure your ingredients precisely.
- To make sure that all of the components are dispersed evenly, the glaze must be properly mixed. Until the glaze is smooth and lump-free, gently and constantly stir the mixture.
- The glaze’s consistency has an impact on how it will flow and stick to the pottery, thus it is crucial. In general, a glaze should be thick enough to adhere to the surface without dripping while being thin enough to flow easily. It’s vital to test the glaze on a little, unnoticeable piece to make sure it’s the proper consistency because the ideal consistency might vary based on the glaze recipe and the type of pottery you’re decorating.
- You can add a little quantity of water to the glaze to thin it out if it is too thick. You can thicken the glaze by adding more glaze powder or other ingredients if it is too thin.
- To make sure the glaze is the proper color and consistency before using it on your pottery, test it on a small, unnoticeable piece. You can avoid any unforeseen circumstances or issues by doing this.
Advantages Of Underglazing
A pottery item can benefit from underglazing in a number of ways.
- Underglazes can provide a more strong, brilliant shade of color than overglazes since they are designed to stick to clay properly. This is particularly helpful when making intricate designs or using strong, vivid color combinations.
- Underglazes are fired at a lower temperature than overglazes, which increases their resistance to chipping and scratching.
- Underglazes can be blended and stacked to produce a variety of hues, designs, and textures. Additionally, they can be utilized to produce designs that can be easily revised or touched up after the initial firing.
- Using an underglaze can give pottery more depth and dimension because it can settle into the clay’s fissures and fractures to give it a more textured, organic appearance.
- Underglazes act as a barrier between the clay and any later-applied overglaze or ornamental components, preventing harm to the pottery.
Disadvantages Of Underglazing
While applying an underglaze on ceramics has numerous benefits, there are also some potential drawbacks to take into account.
- Applying an underglaze can be more difficult and time-consuming than using an overglaze since the potter must first coat the item with the underglaze, let it dry, and then fire it before adding any further glazes or ornamental accents.
- Some underglaze color selection restrictions may make it challenging to create specific hues or tones.
- Multiple firings are necessary when using an underglaze, which can be more time-consuming and expensive than using a single firing technique.
- Because not all underglazes are appropriate for all types of clay or glazes, potters must be careful to select the best underglaze for their unique requirements.
- The effect of firing an underglaze can change depending on a number of variables, including temperature, kiln atmosphere, and firing time. As a result, getting consistent results from one firing to the next may be challenging.
What Is The Difference Between Underglaze Decoration And A Transparent Glaze?
Transparent glaze and underglaze ornamentation are two types of glazes used in pottery manufacturing.
Before the pottery is fired, underglaze decoration is a form of glaze that is put to the surface. It is designed to attach effectively to the clay and is typically fired at a lower temperature than other glazes. Underglaze decorating is frequently used to produce complex patterns, vivid colors, and detailed motifs. It can be stacked to produce a variety of effects.
Transparent glaze is a kind of glaze that is placed to the pottery’s surface and is made to be transparent or translucent. It is used to give the pottery a smooth, glassy surface and is often fired at a higher temperature than underglaze ornamentation. By imparting a layer of sheen and protection to the pottery’s surface, transparent glazes can also be utilized to accentuate the hues and patterns produced by underglaze decoration.
What ceramic raw materials are needed to create an underglaze or a transparent glaze?
Several raw ingredients are often required to manufacture an underglaze or a clear glaze for use in ceramics.
The primary component of many glazes is frit, a form of glass that is melted and powdered into a fine powder. It offers the melting and binding qualities required to produce a glaze that will stick to the pottery’s surface.
Both transparent glazes and underglazes may contain trace amounts of clay, which enhances the glaze’s adhesive qualities and gives it body.
To impart color to glazes, oxides like iron oxide or cobalt oxide are frequently applied.
Alumina is a sort of ceramic substance that is frequently used to glazes to help regulate the glaze’s melting and flowing characteristics.
Used to increase the hardness and durability of glazes, silica is another typical constituent.
To aid increase glazes’ stability and stop them from cracking or crazing during firing, barium carbonate is frequently added.
Adding soda ash to glazes can assist manage their melting characteristics and enhance their flow and leveling qualities.
Depending on the intended properties of the glaze and the type of pottery it will be used on, the precise components and ratios utilized to make an underglaze or a clear glaze will vary. Potters frequently experiment with various components and recipes to discover the blend that best suits their own requirements.
Is There A Difference Between Engobe And Colored Slips?
Although both engobe and colored slips are ornamental finishes used in pottery production, there is a distinction between the two.
Engobe
Before the pottery is fired, a sort of clay slip called an engobe is put to its surface. It is designed to stick strongly to the clay and to smooth out the surface so that glazes or other ornamental elements can be applied. Although less thick and opaque than colored slips, engobes can also be used to impart color or texture to pottery’s surface.
Colored Slip
On the other hand, colored slips are used to produce strong and brilliant colors on the surface of the pottery. They are thicker and more opaque than engobes. After the pottery has been bisque fired, colored slips are often added to the surface. They can be used to produce elaborate shapes and patterns or to give the pottery a solid base color.
Are High-Clay Slurries Generally Light-Colored Or Dark Colored For Use With An Underglaze?
Since white, fine-grained clay is used to make high-clay slurries, they are often pale in color. When an underglaze is placed to the surface, the real colors of the underglaze can be seen through this light color.
Underglazes are ceramic glazes that are used as a base coat and fired at a lower temperature than the primary glaze. Typically employed to produce vivid and colorful designs as well as to protect the porous, bisque-fired clay body, they are applied on the latter. The high-clay slurry’s light shade offers a neutral basis that doesn’t obstruct the underglaze’s genuine hues.
It’s crucial to remember that additional materials, including as low-fire glazes and engobes, which are similarly light-colored, can be utilized to make a base that is appropriate for underglazes. The particular project and the desired outcome will determine the base material to be used.
When Using Slip, Can Detailed Drawings Be Made Easily Or Is This Difficult To Do?
Slip is a fluid material that can be tricky to manage and manipulate, making it difficult to make intricate drawings with it. Slip is a thin clay and water combination that is applied to surfaces to decorate or bind clay pieces together. Its creamy, silky texture makes it challenging to hold delicate details or sharp edges.
Having said that, some skilled potters and ceramicists have discovered methods for using slip to create intricate designs. The use of specialized equipment, such as stamps or templates, to make repeatable patterns or the use of slip-trailing techniques to produce fine lines and designs are a few examples of these approaches. In addition, some artists apply slip in a pattern on a surface as a resist before carving or etching into it to expose the clay underneath.
The level of detail that can be accomplished using slip ultimately depends on the artist’s talent and expertise, as well as the kind of slip and the techniques employed. Slip can be used to produce detailed drawings; however, it may take some trial and error and practice to get the desired results.
How To Know When An Overglaze Should Be Used Instead Of A Slip Or An Underglaze Finish?
Several variables, including as the desired appearance, the kind of clay and glaze being used, and the firing temperature, influence whether an overglaze, slip, or underglaze finish should be employed.
An overglaze is a glaze that is layered over another glaze that has already been fired. Overglazes, like as crackle glazes or luster glazes, are frequently employed to add decorative accents or to provide a specific surface effect. To prevent melting or distorting the underlying glaze, they are often fired at a lower temperature than the main glaze.
A slip is a thin clay and water combination that is applied to a surface to decorate it or to bind clay pieces together. A bisque-fired clay body will typically have slips put to it before being fired once more. They are frequently employed to add aesthetic features or to uniformly color or texture a surface.
Before the main glaze, an underglaze is a glaze that is placed to a porous, bisque-fired clay body. Underglazes are employed to both protect the clay body and provide vivid, colorful motifs. They are often fired at a lower temperature than the primary glaze and typically added over a light-colored high-clay slurry.
Depending on the intended outcome, an overglaze, slip, or underglaze finish can be used. An overglaze is perhaps the best choice if the intention is to embellish a previously fired glaze. A slip might be an excellent option if the objective is to provide a surface a consistent color or texture. An underglaze can be the finest choice if the intention is to produce vivid and colorful graphics.
What Techniques Can Be Employed When Firing Pottery Pieces That Have Been Decorated With Slips, Engobes, Or Underglazes?
There are numerous methods that can be used to achieve the greatest results when firing ceramic pieces that have been decorated with slips, engobes, or underglazes. Some of these methods consist of:
To prevent the clay object from splitting or deforming, a slow firing process is essential. This is crucial when burning items ornamented with engobes or underglazes since they are more porous and susceptible to thermal shock.
Another crucial element in firing ceramics adorned with slips, engobes, or underglazes is controlled cooling. In order to reduce the possibility of cracking and warping and to make sure that the colors stay true and brilliant, a slow and controlled cooling process can be used.
Depending on the kind of clay being used and the kind of glaze or decoration being utilized, the firing temperature will change. In order to guarantee that the glaze or decoration will attach properly and yield the intended results, it is crucial to stick to the appropriate firing temperature for the particular type of clay and glaze being used.
The firing environment, whether reduction or oxidation, can also have an impact on the pottery’s ultimate appearance. Rich, deep colors and a more textured surface are typically produced by reducing atmospheres, whereas lighter colors and a smoother surface are typically produced by oxidizing atmospheres.
Last but not least, it’s critical to make sure that the glaze or ornamentation being used is appropriate for the clay body and firing temperature. It’s crucial to make sure that the glaze or ornamentation will adhere properly and not crack, crawl, or bubble during the firing process because different clays and glazes have varying firing temperatures and thermal expansion rates.
Conclusion And Summary
In ceramics, clay objects are decorated or finished with slip and or underglaze.
Slip is a thin clay and water combination that is applied to surfaces to decorate or bind clay pieces together. It can be added to a clay body that has already undergone bisque firing and fired once more to give the surface a consistent hue or texture or to add decorative embellishments.
Contrarily, an underglaze is a glaze that is used before the primary glaze on a porous, bisque-fired clay body. Underglazes are employed to protect the clay body while generating vivid, colorful motifs. Typically, they are fired at a lower temperature than the primary glaze and are put to a high-clay, light-colored slurry.
The method they are utilized and the qualities they have are the key distinctions between slip and underglaze. Underglaze is a glaze used to create bright and vibrant designs, whereas slip is a thinner, more fluid material used to create a uniform color or texture. Underglaze is fired at a lower temperature than the primary glaze, while slip is fired at the same temperature as the clay body. In addition, underglaze lasts longer and is more resilient than slip, which can eventually break or fade.
Slip and underglaze are both ceramic decorating techniques, but there are important differences. Underglaze pencils are one type of underglaze, a colored substance applied to clay before firing. Slip, on the other hand, is a mixture of clay and water, used to join two pieces of leather-hard or bone dry clay. Art of Education University recommends using a Mixed Media Applicator Set to apply underglaze, which can be used to create a wide range of effects, including rich earth colors and visual depth.
Slip, however, is an excellent solution for joining two clay pieces together. The Quartz Inversion is a key temperature consideration for both slip and underglaze, as it impacts the strength of the finished piece. Techniques like Mishima and sgraffito can be used with both slip and underglaze to create unique designs. However, underglaze pencils may require a gluing agent, while slip does not. Slip is made from clay and water, while underglaze typically contains glass forming ingredients and fritted materials. Wax resist can also be used with both slip and underglaze to create designs and protect certain areas of the piece.
Epilogue
When it comes to ceramics, two popular ways to add color and design are slip and underglaze. Slip is a liquid clay mixture that can be applied to leather-hard clay to create a textured surface or to add layers of color. Underglaze, on the other hand, is a colored material that is painted onto hard or dry ceramics before being fired. While both can be used for functional or decorative purposes, they have different properties and applications. Slip is made from the same main clay body as the ceramics, while underglaze is a separate material that can be applied to any bone-dry greenware. Slip tends to fire opaque and can be used to create surface texture and visual depth, while underglaze can create rich earth colors and is an excellent solution for intricate designs and detailed work. The firing process can also affect the differences between slip and underglaze. Slip is fired at a lower temperature, while underglaze is fired at a higher temperature to make it more durable. Overall, understanding the difference between slip and underglaze can help ceramic artists achieve the desired effect in their creations.
References
By Zereshk – Metropolitan Museum of Art, CC BY-SA 3.0 Composite body, painted, and glazed bottle. Iran, 16th century (Metropolitan Museum of Art)
By Photograph by Clem Rutter, Rochester, Kent. (www.clemrutter.net). Part of a mold for making a teapot
By Coyau / Wikimedia Commons, CC BY-SA 3.0, Removing the last parts of a mold from a slip casting
By Photo: Myrabella / Wikimedia Commons, CC BY-SA 4.0,
Some of the shapes made in the small-scale slip casting workshop of the manufacture nationale de Sèvres
