What Would Make Clay Blue?

Clay is a unique and versatile material. It is composed of fine-grained minerals such as kaolinite that give it its plasticity. This allows clay to be molded into various shapes when wet, and retain its form when dried and fired in a kiln. Clay comes in a range of natural colors including red, brown, grey, and white, depending on its mineral composition.

The color of natural clay can be modified through various techniques to achieve different aesthetic effects. By adding colorants and firing clay at specific temperatures, potters and ceramicists can create clay in vivid hues like blue. The process of artificially coloring clay requires an understanding of clay’s properties and how it interacts with metal oxides and other colorants.

This article will provide an in-depth look at how to produce blue colored clay. We will cover common natural clay colors, the chemistry behind clay’s color, methods for artificially coloring clay blue, how to fire blue clay properly, and the history of blue-glazed ceramics.

Natural Clay Colors

Clay comes in a wide range of natural colors depending on its mineral composition. The most common natural clay colors are red, brown, white, and grey. The specific colors result from impurities mixed within the clay during its geologic formation.

Red and brown clays get their color from iron oxide. The amount of iron oxide determines how red or brown the clay is. Clays with higher iron oxide content are a deeper red, while clays with less iron oxide are a lighter brown. White clay lacks iron oxide and other colorants, giving it a bright white appearance. Grey clay also lacks iron oxide but contains carbonaceous materials that darken its color.

The mineral content of clay can vary significantly between deposits, leading to this wide variation in natural color. Even within a single deposit, natural clays can exhibit color variation due to changes in mineral composition across the deposit.

How Clay Gets Its Color

The natural color of clay comes from the minerals and metals present in the soil it is formed from. Iron oxide in the soil results in red and brown shades of clay, while calcium carbonates produce white and light colored clays. Other mineral deposits and metals contribute additional colors and variations.

As clay is weathered and washed downstream it picks up different combinations of minerals that determine its final color. Clays with high iron content are redder, while those with more calcium are whiter or lighter shades. The unique composition of the soil clay forms in lends it a distinctive natural color.

Artificially Coloring Clay

Clay can be artificially colored with stains/pigments to achieve brighter, more vibrant hues than what occurs naturally. Artificial coloring gives the potter or ceramicist greater control and creativity over the look of finished ware. Rather than being limited by the natural clay colors of a region, artificially colored clays allow artists to produce pieces in any color they desire.

Some key advantages of artificially coloring clay versus using natural clays colors:

• Much wider range of colors – blues, greens, purples, reds, etc.
• Consistency – hand mixing stains into clay allows controlling color consistency across batches
• Intensity – stains permeate the clay body better than natural impurities, allowing deeper, more vibrant hues
• Aesthetics – man-made colors allow more creativity and personal expression
• Special effects – colored clays can be blended, marbled, or mixed for unique looks not found naturally

Artificially coloring clay with stains gives ceramic artists great flexibility when deciding on the look of their pieces. It opens up creative possibilities not available from regionally sourced natural clay deposits.

Making Blue Clay

Blue clay does not occur naturally. To create blue colored clay, cobalt oxide or copper carbonate is typically added and mixed into the clay body before firing. When the clay mixture is fired at a high enough temperature, the cobalt oxide or copper carbonate reacts and turns the clay blue.

Cobalt oxide is one of the most commonly used materials to make blue colored clay. It produces a brilliant blue color in stoneware and porcelain clays. The more cobalt oxide added, the darker and more intense the blue color will be. Copper carbonate can also be used to produce blue clay, but it tends to create more greenish blue tones compared to cobalt.

The blue clay mixture needs to be fired to at least 1200°F (650°C) for the chemicals to react and create the blue color. The clay also needs to be fired in a reduced oxygen environment. This reduction atmosphere helps drive the chemical change that occurs during firing to produce the blue color.

Making blue colored clay requires careful testing and control of the clay ingredients, chemical additives, and firing conditions. But when done right, beautiful vivid blue ceramics can be achieved.

Other Ways to Color Clay Blue

In addition to adding cobalt to the clay body, there are other techniques ceramic artists can use to make blue clay or blue glazed finishes on ceramics:

Blue Underglazes, Stains, and Pigments

Underglazes are products containing colored ceramic pigments that can be applied to bisqueware clay before glazing and firing. Blue underglazes are available in a wide range of shades. Underglazes will produce a matte finish.

Blue ceramic stains contain concentrated amounts of coloring oxides and can also be applied before glazing to achieves deep saturated blue colors. Stains fuse into the glaze during firing.

Blue ceramic pigments can also be used by mixing them into a clear glaze base or other glaze recipe to tint the entire glaze blue.

Mixing Blue Sand, Grog, or Slip

Adding blue-colored sand, grog (ground fired clay particles), or slip (liquid clay) when wedging or mixing a clay body is another way to produce blue colored clay. The blue particles will distribute through the entire clay body and remain after firing. Sand or grog can produce speckled effects while slip will make the clay a solid blue color.

Firing Blue Clay

The temperature at which the clay is fired can significantly affect the final color and shade of blue clay. When firing blue clay, it’s important to pay close attention to the firing schedule and target temperatures.

Most blue clays reach their peak blue color in the mid-range temperatures (cone 04-06, approximately 1945-2165°F). Firing too low, below cone 06, may result in a more muted, greyish shade of blue. Firing higher, approaching cone 10 temperatures (approximately 2345°F), can cause the blue color to turn darker and start to burn out, shifting towards black or grey tones.

The mineral composition and specific type of blue clay will determine the precise firing range for optimal blue tones. But in general, mid-range temperatures between approximately 1000°C and 1200°C (1830-2190°F) produce the most vibrant blue hues.

Test tiles are highly recommended when firing blue clay to fully understand its firing range and color progression. Keeping detailed notes and firing records will help reproduce the ideal blue colors. A pyrometer can precisely monitor the kiln temperatures during firing.

With care and by following the proper firing schedule, beautiful and consistent shades of blue clay can be achieved.

Uses of Blue Clay

Blue clay has become popular for decorative uses due to its eye-catching color. Here are some of the common uses for blue colored clay:

Decorative pots, tiles, jewelry – Blue clay is often used to make decorative pots, tiles, vases, plates, and jewelry. The vibrant blue color makes these items stand out. Blue clay pottery and tiles can add a unique pop of color to gardens, kitchens, bathrooms, and other areas of the home.

Novelty blue bricks, sculptures – Blue clay is also used to make novelty bricks for gardens or paths. Sculptors may also choose to work with blue clay to make unique sculptures that draw the eye. While not as common as red clay bricks, blue clay bricks and sculptures can add whimsy and visual interest to outdoor areas.

Blue Clay in History

The use of blue clay dates back thousands of years to some of the earliest human civilizations.

The earliest known blue glazed pottery was developed in ancient Mesopotamia (modern day Iraq) around 2500 BC. Artisans learned to create vivid blue and turquoise glazes using copper oxide. This Mesopotamian pottery was traded widely and influenced ceramic techniques across the Middle East and Mediterranean.

In ancient Egypt, blue glazed faience (a ceramic material) was developed around 1500 BC. Egyptians glazed beads, amulets, tiles and other objects in bright blue colors using copper. The famous King Tutankhamun was buried around 1330 BC with blue glazed shabti figurines placed in his tomb.

China also developed sophisticated blue glazing techniques very early on. As far back as the Shang dynasty in 1600 BC, Chinese potters used cobalt blue pigments imported from Persia to create blue decorated porcelain. In the Tang dynasty around 600 AD, Chinese artisans invented cobalt blue on white glazed porcelain, which became extremely popular for export around Asia and Europe.

So the use of blue clay and glazes dates back over 4,000 years, with early civilizations innovating techniques to create vibrant blue ceramics and pottery.

Conclusion

Making clay blue can be achieved in a few different ways. Coloring agents like cobalt oxide, copper carbonate, or even blue food coloring can be added to natural clay to create a vibrant blue color. These colorants can be kneaded directly into the raw clay body or mixed into a clay slip to dip or paint onto bisqueware. Blue glazes are another option, made by incorporating cobalt oxide into the glaze recipe and resulting in a glossy blue finish after firing. While chemical additives are the most direct route, natural clays with higher iron content can also fire to a blue or blue-green shade.

Once you have blue clay, whether natural or artificially colored, the possibilities for creativity are endless. Blue clay can be sculpted into pottery, figurines, beads, tiles, and more. Many cultures have a history of using blue clay for decorative and functional wares. When fired, blue clay maintains its vivid color, making it eye-catching for artwork, dishes, or building materials. With the right coloring agent and firing technique, blue clay can be incorporated into your own unique ceramic creations.