Burnished clay refers to clay that has been polished or rubbed to create a smooth, shiny surface. The specific color of burnished clay can vary greatly depending on the clay body composition and firing temperature. However, there are some general color characteristics that are common for burnished clays.
The burnishing process brings out the natural colors of the clay body in a richer, deeper way. It also enhances color effects from any stains, oxides, or pigments that have been mixed into the clay. So the resulting color depends heavily on the base clay color and any additives.
Some of the most common colors seen in burnished clay are warm earth tones like tan, brown, terra-cotta red, and russet orange. Burnished clay can also display cool greys, blacks, buff shades, pale blues, and olive greens depending on the clay ingredients.
The firing temperature has a major impact on the final burnished clay color. Lower fire clays (up to cone 04 or 1945°F) tend to keep their natural clay colors. Higher fire clays (cone 5-10) develop more intense, saturated colors as mineral components in the clay melt and react.
Factors that Influence Burnished Clay Color
There are several key factors that determine the final color outcome for burnished clay:
– Base clay composition – The natural color of the clay body before any additives makes a big difference. Red and brown clays will produce warm, earthy burnished colors. White and buff clays create paler, neutral colors. And black, blue, or olive-colored clays result in cooler, darker burnished finishes.
– Firing temperature – How hot the burnished clay is fired significantly affects the colors. Low fire keeps natural clay colors muted. Mid-range fires (cone 04-5) deepen and saturate colors. High fire (cone 6-10) produces more intense, dramatic colors with greater color variation across the surface.
– Clay additives – Adding stains, oxides, pigments, or grog (ground fired clay) alters the base color. Red iron oxide produces rusty red-browns while cobalt carbonate creates blue-grays. A dolomite additive results in warm pinkish tan.
– Burnishing method – The technique used to burnish the clay impacts the color depth and shine. Aggressive burnishing creates darker colors and more reflectivity. Lighter burnishing maintains more of the natural clay color with a satiny luster.
– Firing atmosphere – Firing in oxidation produces warmer, lighter colors with more color variation. Reduction firing gives more uniform, darker colors with grayish undertones. Soda firing can create mottled surfaces with metallic sheens.
– Glazes – Applying a translucent glaze over burnished clay affects the underlying color. Glazes tint and unify the color while muting variation. Clear glazes enhance shine without altering color much.
Typical Burnished Clay Colors
Here are some of the most common colors achieved with burnished clay depending on the clay type and firing temperature:
Red Clay
– Terracotta
– Rust red
– Rose brown
– Tomato red
– Brick red
– Copper red
Brown Clay
– Tan
– Caramel
– Mocha
– Milk chocolate
– Dark chocolate
– Coffee brown
White Clay
– Cream
– Buff
– Bisque
– Bone white
– Ash grey
– Dove grey
Black Clay
– Charcoal grey
– Blue black
– Jet black
– Gunmetal
– Dark olive
– Graphite
Multi-Colored Clay
– Tortoiseshell patterns
– Speckled
– Mottled
– Veined
– Ombre gradients
– Metallic shimmer
The specific clay composition makes a significant difference in the range of colors possible. But various application techniques and firing environments allow diverse colors to be achieved with most clay types.
How to Create Specific Burnished Clay Colors
If aiming to produce burnished clay in certain hues, here are some tips:
Warm Earth Tones
– Start with a red or brown clay body
– Add red iron oxide or mix in a red clay additive
– Burnish aggressively before bisque firing
– Use an oxidation atmosphere in the kiln
Cool Neutral Tones
– Choose a white or grey base clay
– Add small amounts of black, blue, or green stains
– Bisque fire then burnish lightly to a satin sheen
– Use a reduction atmosphere during glaze firing
Deep Jewel Tones
– Mix in cobalt carbonate for blues and greens
– Add copper carbonate for aqua turquoises
– Try chrome oxide for emerald greens
– Burnish vigorously before glaze firing above cone 6
Metallic Shimmers
– Apply mica powder, gold leaf, or silver leaf
– Burnish strongly, then glaze with a transparent clear
– Frequent polishing during firing helps develop the metallic look
Mottled, Variegated Colors
– Roll out clay in a slab then twist and pinch it
– Burnish the raised sections more than the recessed parts
– Firing in soda can create splotchy surfaces
– Apply translucent glazes lightly for subtle effects
With thoughtful clay choices and test tile experiments, a wide spectrum of burnished clay colors can be perfected.
How Burnished Clay Gets Its Color
The polish from burnishing reorients clay particles, compresses the surface, and creates a smooth, aligned finish. This enhances the natural color of the clay. Burnishing also pushes any colorants and additives near the surface yielding saturated, vivid colors.
Here are the key mechanisms that produce color in burnished clay:
– Base clay minerals – Iron, calcium, magnesium, and carbon compounds in clay produce warm earth tones from cream to red to brown.
– Stains and oxides – Inorganic compounds like cobalt, copper, chrome, manganese oxides create specific colors from blue to green to orange when concentrated at the surface.
– Firing atmosphere – Oxidation firing produces lighter, warmer colors. Reduction kilns yield more grayish, unifying tones with less color variation across the surface.
– Glazes – Clear glazes intensify existing colors. Opaque glazes cover the base color with their own. Translucent glazes filter and mix the burnished color with the glaze color for gradients.
– Carbon displacement – where clay meets the kiln shelf, carbon is drawn out leaving grey or black banding effects.
– Flashing – crumpling and pinching clay before burnishing creates color flashes from folded sections firing differently than exposed ones.
– Termination crystals – some glazes produce small color burst crystals where the glaze stops, enhancing color effects.
So burnished clay derives its hues from the base clay, embedded colorants, firing methods, and finishing processes. Mastering the variables allows ceramic artists to create their desired burnished color palette.
Conclusion
Burnished clay takes on a wide spectrum of colors from neutrals to earth tones to vivid jewel tones. The natural clay composition, additives mixed in, and finishing techniques all contribute to the final burnished color. Firing temperature and atmosphere also affect the colors.
While the colors span a broad range, burnished clay typically displays rich, deep colors with a high-gloss, reflective surface. The burnishing process concentrates colorants near the surface and compresses the clay into a tight, smooth face. This empowers the natural clay ingredients to reveal their strongest colors.
With knowledge and experimentation, ceramic artists can produce burnished clay in precise hues. From warm terra cottas to cool charcoal greys and everything between, burnished clay offers an endless diversity of color possibilities.
