Can You Make Colored Slip With Underglaze?
What is Slip?
Slip is a liquid clay suspension used in ceramics and pottery for various purposes. It has a creamy consistency similar to heavy cream or pancake batter. Slip is made from clay powder mixed with water to create a pourable and smooth mixture.
There are several types of slip commonly used:
- Casting slip – Used for slipcasting, has higher plasticity and viscosity.
- Terra sigillata – A refined slip used for surface finishes, has very fine particle size.
- Regular slips – Used for decoration or adhesion, moderate viscosity.
The composition of slip consists of:
- Clay – Usually a very plastic clay high in kaolinite.
- Water – Added to dissolve the clay into liquid form.
- Deflocculants – Chemicals to break up clay particles and prevent flocculation.
What is Underglaze?
Underglaze is a colored clay product used to decorate pottery and porcelain. It is applied to raw clay surfaces before the piece goes through a final firing or glaze firing. Underglaze differs from glaze in several ways:
Definition of underglaze: Underglaze is mixed with water and brushed onto leather-hard or bisque clay. The clay piece is fired, which permanently affixes the underglaze. A clear glaze may then be applied over the top and the piece fired again.
Types of underglaze: There are two main types of underglaze – regular underglaze that can be fired to cone 08-04, and a high fire underglaze that can be fired up to cone 6. Underglaze comes in a variety of colors and finishes like glossy, matte, translucent, and opaque.
How it differs from glaze: Glazes contain glass-forming ingredients that create a glassy coating on clay at high temperatures. Underglazes do not form a glassy surface. They are made of stable metal oxide pigments suspended in a flux. The flux allows the underglaze to adhere to the clay after firing. Underglaze also differs in application – it goes on raw clay while glaze is applied after bisque firing.
Benefits of Colored Slip
Using colored slip provides many benefits for ceramic artists and potters. Some of the key advantages of incorporating colored slip into your pottery process are:
Decorative Effects
Colored slip enables endless decorative options. You can paint slip onto bare clay or bisqued pieces to add splashes of color, intricate patterns, gradients, and more. The slip maintains its vibrancy after firing, allowing you to permanently decorate your pottery.
Color Variation
Slip comes ready-made in a huge array of colors, from neutrals to bold hues. You can also easily mix custom colors. This makes colored slip ideal for adding layers of color interest to your pieces. The color possibilities are endless.
Textural Interest
Beyond flat color application, colored slip can also provide appealing textural effects. You can trail, drip, sponge, or stamp the fluid slip onto clay to create visual depth and dimension. The colored slip maintains any texture after firing for added visual interest.
Making Colored Slip
Making your own colored slip at home is easy with just a few ingredients. Here’s what you’ll need:
- White slip – This forms the base of your colored slip. You can purchase ready-made white slip or make your own using clay, water and deflocculant.
- Underglazes – These colored glazes are used to tint the white slip. Use underglazes specifically designed for slip.
- Water
- Measuring cups
- Mixing containers
- Mixing sticks
Start by measuring out the white slip into your mixing container. The amount depends on how much colored slip you need to make. For deep saturated colors, use less white slip.
Next, add underglaze to the white slip starting with small amounts like 1-2 tsp per cup of slip. Mix thoroughly until the color is even. Add more underglaze for a deeper color. Remember you can always add more color, but you can’t take it away!
Finally, thin the colored slip with water as needed to reach a creamy consistency – about like heavy cream. The slip should flow evenly but not be watery. Test the consistency on a piece of bisqueware to ensure it applies smoothly.
Once your slip is mixed, store any leftovers in a sealed container. Colored slips can be kept indefinitely and reused.
Adding Underglaze to Slip
When adding underglaze to slip, there are a few tips to follow for best results:
Use a cone 06-04 underglaze specifically formulated for adding to slip. These have compounds that interact well with the slip chemistry. Avoid using stroke-and-fill or highfire underglazes, which may cause crawling or other issues.
Start with a 10% ratio of underglaze to slip. For example, mix 1 part underglaze to 10 parts slip by weight. The underglaze percentage can be adjusted up or down depending on the desired intensity of color.
Make small test tiles with underglaze slip mixtures before applying to pieces. Test different underglaze percentages and combinations. Allow test tiles to dry fully and fire to the intended temperature. The fired tests will show the real color and verify the mixtures work as expected.
Keep mixing and testing until the perfect colored slip recipe is developed for your project. Make notes on the mixtures and keep records of what works. With some experimentation, beautiful custom colored slips are achievable.
Applying Colored Slip
There are a few different techniques you can use to apply colored slip to your pottery pieces:
Brushing
Using a soft bristle brush, you can brush colored slip onto your piece in broad strokes. Brushing allows you to control the desired texture and thickness of the colored slip. It’s great for adding accents and highlights.
Dipping
For an even coating of colored slip, you can dip your piece into a container filled with slip. Fully submerge and gently swirl or rotate your piece to allow the slip to fully coat the surface. Let any excess drip off before setting aside to dry.
Pouring
For a fluid, flowing effect, you can pour colored slip directly onto your piece. Tilt and turn your piece to guide the slip around the surface. It will naturally pool and drip creating organic patterns.
Layering Colors
You can layer multiple colors of slip to create color blending effects. Apply the first color and let fully dry. Then add additional colors on top. The layers will interact creating new hues and visual depth.
Drying and Firing
After applying your colored slip to your ceramic piece, you’ll need to allow adequate dry time before firing. The drying time will vary based on the thickness of your slip application, the clay body, and the environmental conditions.
In general, allow colored slip applications to dry 24-48 hours before handling. Make sure the slip has dried evenly without cracking before firing. Uneven drying can cause flaws. Ensure slip is completely dry by checking for any cool, damp areas.
When firing colored slip, follow the recommended firing schedule for the clay body and glazes used. Fire no faster than the clay and glaze manufacturer specifications. Typical cone 04-6 colored slip firings range from 1922°F (1050°C) for cone 04 low-fire pieces, to 2165°F (1185°C) for cone 6 stoneware and porcelain.
Firing too slowly can cause underfired work. Firing too quickly can cause blistering issues. Carefully follow the firing schedule and make sure to use proper ventilation in your kiln. Test fire sample pieces to dial in the optimal firing for your clay and glazes before firing finished works.
Tips and Tricks
When working with colored slip, there are some tips and tricks to keep in mind for avoiding common issues like cracks and achieving a smooth finish.
Avoiding Cracks
Cracks can occur in colored slip for a few reasons. To prevent cracks:
- Make sure the slip is mixed to a creamy, velvety consistency – too thin and it will be prone to cracking.
- Apply multiple thin layers of slip rather than one thick layer, allowing each layer to dry in between.
- Avoid applying slip too thickly in detailed areas.
- Allow greenware to dry slowly and thoroughly before bisque firing.
Achieving Smoothness
For best results with a smooth slip finish:
- Use a rubber rib or soft rubber kidney to compress each layer and smooth out brush strokes.
- Lightly sand any bumps with 400 grit sandpaper between layers.
- Wipe down each layer with a damp sponge before applying the next.
- Use a very soft paintbrush to gently blend and feather edges.
Fixing Mistakes
If any cracks, bumps, or unevenness occur:
- Let the piece fully dry and fill in cracks by applying slip with a small brush.
- Sand down any bumps or ridges.
- Apply a thin layer of slip overall to smooth everything out.
Paying attention to these tips will help avoid frustration and create smooth, professional colored slip finishes.
Design Possibilities with Colored Slip
Colored slip opens up many exciting design possibilities when decorating pottery. Here are some ideas to spark your creativity:
Patterns
Slip lends itself beautifully to pattern work. Consider using slip to create geometric patterns, organic shapes, or repeating motifs like dots, stripes, and more. Layer colors and patterns for added visual interest.
Contrasts
Play with contrasting colors of slip to make designs pop. Try bold black slip on white clay for high contrast. Or use complementary colors like orange and blue slip together. Contrasting slip colors also look great on etched, carved, or imprinted clay surfaces.
Textures
Experiment with different slip textures and effects. Try a cracking slip effect for an aged look. Use thick slip for impasto textures. Or make trailing slip lines and drips for fluid textures. Combine glossy and matte slips for more visual variety.
Examples of Finished Pieces
Colored slip can create beautiful effects on finished ceramic pieces. Here are some examples of works using colored slip and descriptions of the techniques used:
Botanical Vase
This vase features a flowing botanical pattern in blue colored slip on a white background. The blue slip was painted on leather-hard clay in an impressionistic style.
Geometric Planter
Striking geometric patterns in blue and white colored slips decorate this planter. The slips were painted on with fine tip brushes in graphic designs before bisque firing.
Southwestern Style Bowl
This colorful handmade bowl features a Southwestern-inspired pattern in blue, red, and white colored slips. The slips were carefully hand-painted to create the intricate design.
