SURFACE DESIGN AND TECHNIQUES Engobes/Underglazes
We have explored plain slips, applied to wet or leather-hard work. As you
know, slips made from unmodified claybody recipes are not appropriate for
application to bone-dry or bisque-fired work. We have an opportunity for
experiments with underglazes or engobes. Engobes refer to any slip formulated
for application to bone-dry or bisque-fired wares, while underglazes
specifically refers to slips that are mixed thickly and are very strongly tinted
with stain, so that even a thin application gives strong color. The nature and
performance of an engobe or underglaze lies somewhere between a plain clay
slip and a glaze. Glazes are of course formulated to be applied to bisque-fired
wares without peeling or flaking as they dry on the surface. Engobes or
underglazes are simply specially-formulated slips containing higher
percentages of non-plastic materials (calcined clay and/or additional silica and
feldspar), which reduce drying shrinkage, and create a strong bond with the
surface during the firing.
Thanks to Vince Pitelka for this lovely description!
Normally, in ceramics the term “stain” refers to a fritted colorant, as in Mason
stains or a metallic oxide, such as iron oxide. In using stainas, it is as used in
painting houses and furniture, where it implies a transparent, colored patina that
allows the texture and some of the color of the substrate to show through. An
oxide stain is usually a simple mix of ceramic coloring oxide and water,
although it sometimes contains a small amount of frit to help flux the colorant
to the substrate. Similar stains can also be made by mixing ceramic stains like
Mason stains with water, often with a frit included as well. These media are
different from glaze in that they are primarily just colorant in water, and thus
are applied very thinly. Oxides along on a surface are never food safe.
It is easy to be confused by these terms. The term oxide stain is easy to
recognize, but how do we refer to a similar mixture containing a commercial
ceramic stain colorant? For clarity’s sake, we will call them ceramic stain
patinas, but remember that oxide stain uses the term stain in the sense of a thin,
transparent coating, while ceramic stain patina uses the term stain in the sense
of a commercial fritted ceramic stain colorant.
Oxide stains and ceramic stain patinas can enliven the ceramic surface and
introduce color with little or no glaze. They can be applied overall to modify
the appearance of a glaze. They can also be applied selectively with a stamp,
brush, or airbrush to create imagery under or over the glaze. On textural
surfaces, an oxide stain or ceramic stain patina can be brushed overall on the
raw bisque surface and then sponged off the high spots in order to accentuate
the texture, with or without a glaze. An oxide stain or a ceramic stain patina
applied overglaze by spray, brush, spatter, or sponge-stamp can modify the
glaze color locally and create interesting effects.
When applying a patina to a piece that will otherwise remain unglazed, it is a
good idea to use a fluxed patina that contains some clear glaze, gersley Borate
or Ferro 3134 frit as a flux or melter, which will make the colorant fire hard
and adhere to the clay surface. This is especially important at low-fire
temperatures, as otherwise oxides or stains will remain dry and powdery on the
surface after the firing. Up to 50% frit or glaze may be added, but the more
you add, the shinier the surface will be, especially where it remains thicker in
recessed areas. In some patinas, a zircon opacifier or tin oxide may be added to
give a more opaque deposit of patina in the recessed areas.
Even without coloring oxides or ceramic stains, a very thin application of a
watered down glaze or a watery mixture of 3134 frit can act as a patina to
produce a wetting effect and even a slight sheen on the surface, intensifying
color and visual texture. While inappropriate for utilitarian surfaces, this may
be an ideal finish for sculpture or non-utilitarian vessels, especially over
complex slip, engobe, or underglaze decoration, since glaze can often mute the
effects of painterly slip application.
An interesting variety of patina in ceramics are those which simply
approximate the accumulation of dirt and debris found in much ancient
claywork. Varying proportions of zircon opacifier or tin oxide and coloring
oxides with some 3134 frit (to flux the patina onto the surface) will give a
range of “dirt” colors from light to dark brown or black. Following are a range
of sample patina recipes using oxides, opacifiers, and frit.
Dry Patinas - for a dry, earthy effect, intended to imitate the accumulated
residue in the recesses of ancient wares. Should not be used on any surface
which comes in contact with food. Amounts are proportional by weight. Mix
all patinas with water to a thin milky consistency.
Black - 3 manganese dioxide, 3 red iron oxide, 2 cobalt carbonate, 2
Ferro 3134 frit.
White - 8 tin oxide, 2 Ferro 3134 frit.
Dirt - 5 tin oxide, 1 copper carbonate, 2 red iron oxide, 2 Ferro 3134
frit.
Copper - 4 tin oxide, 4 copper carbonate, 2 Ferro 3134 frit.
Iron - 8 red iron oxide, 2 Ferro 3134 frit.
Gloss Patinas - for a glossier finish, especially where thicker, as in corners and
recesses. Should not be used on any surfaces which comes in contact with
food. Amounts are proportional by weight.
Black - 2 manganese dioxide, 2 red iron oxide, 1 cobalt carbonate, 5
Ferro 3134 frit.
White - 5 tin oxide, 5 Ferro 3134 frit.
Dirt - 2 tin oxide, 1 copper carbonate, 2 red iron oxide, 5 Ferro 3134
frit.
Copper - 3 tin oxide, 2 copper carbonate, 5 Ferro 3134 frit.
Iron - 5 red iron oxide, 5 Ferro 3134 frit.
Wax-based Patinas
Oxides and/or glazes may be mixed with wax resist and used for brushed or
stamped decoration on the bare clay or over a previously applied glaze. In
applying a subsequent glaze, this mixture will both provide color and resist the
glaze. If this mixture is to be applied over bare clay, add a little dry powdered
glaze or 3134 frit to bond the oxide in place in the firing. When used on bare
clay, the amount of glaze or frit added will determine how shiny the oxide
surface is after the firing.
A lesser-known use of wax-based oxide stains or ceramic stain patinas is found
in the technique known as Cuerda Seca. In this technique, oxides or ceramic
stains and a small amount of glaze or 3134 frit are combined with wax resist as
described above. This mixture is painted onto the surface of a piece to create a
line drawing of a pattern or image. Different colored glazes are painted onto
the intervening areas of bare clay, and the wax in the Cuerda Seca mix resists
the glaze, simplifying application. After the glaze firing the tinted oxide lines
are generally much less shiny than the glazed areas, and the resulting effect
looks similar to tile work with a colored grout line between individual ceramic
tiles.
Glazing
When you decide to glaze a piece, you still have a myriad of possibilities to
consider. In approaching glazes in general we immediately think of color and
shine, but these are just two of many considerations.
Glaze Color
Glaze color alone involves a range of variations including hue, shade, tint,
intensity, and saturation. This is the language used by painters, and for the
most part it is applicable to glaze color. Hue is the actual color, such as red,
blue, orange, etc. A shade of a color is darkened from the median point of light
and dark, usually by the addition of black pigment. A tint of a color is
lightened from the median point, usually by the addition of white. Intensity is
the brightness of the hue; the degree to which it commands attention and seems
to jump off the surface. Saturation is the depth and richness of the color,
resulting from the combination of hue, intensity, and shade or tint.
Glaze Transparency and Surface
When we think of glazes in general, we often assume a gloss surface, but again
this is just one of many options. Glazes are just silica glass with various
modifiers added to affect their behavior and appearance. Depending on the
glaze materials and modifiers present, the glaze can be gloss, semi-gloss, semimatt, or matt. These are all qualities of reflectivity and visual/actual texture,
but variables in the glaze appearance may also include transparency/opacity,
translucency, iridescence, thickness, and mobility (viscosity at maturation
temperature). The most transparent glazes are invariably glossy, because
anything other than a high-gloss surface interferes with
transparency. However, high-gloss glazes often tend to be a bit garish, and will
show every surface flaw. Most potters usually prefer semi-gloss or semi-matt
glazes, which can give a very appealing silky surface texture. Even on a semigloss or semi-matt clear glaze, transparency is hardly diminished, and such
glazes can work extremely well over slip-decorated surfaces, showing the
variations of slip color while maintaining a softer surface quality.
Effects such as translucency, opacity, and iridescence result from either of two
phenomena, or a combination of the two. First, they may result from particles
or globules of inert materials floating within the glaze. Opacity is usually
achieved by adding highly refractory materials such as zircon opacifiers, which
simply remain suspended in the glaze, interfering with transparency, without
effecting any other quality of the glaze. However, if too much of this material
is added it will interfere with proper glass-formation, and the glaze will be dry
and under-fired. Total opacity may be achieved in almost any glaze by the
addition of 10% zircopax (zirconium silicate opacifier) or 5% tin oxide. The
latter is a very expensive material, so we generally use zircopax except in
situations where glaze color responds positively to tin.
The second phenomenon which can produce opacity or translucence is the
growth of crystals within and upon the glaze during the cooling ramp. If the
glaze is cooled too quickly, crystal growth will be minimal. When wishing to
accentuate crystal development, it is a good idea to close the damper entirely at
the end of the firing for at least a few hours and/or soak the kiln between 1900
and 1800 degrees Fahrenheit during the cooling ramp.
Iridescence can result from the presence of an immiscible material such as
phosphorus (usually from bone ash), which produces small globules suspended
within the glaze. As long as the glaze is otherwise transparent, the reflective
surface of these globules can create iridescence, such as is often found in Chun
blue glazes. Iridescence can also result from crystal growth in the surface of the
glaze, as in many “khaki” saturated iron red glazes.
Glaze Effects Resulting from Thickness of Application
Behavior of glazes obviously depends greatly on thickness of
application. Viscosity is a key issue here, and we must anticipate the mobility
of a glaze to insure that it does not run excessively. We know that a thick
application of an opaque glaze will conceal any subtleties in actual texture, and
may run all over the place. Inversely, a very thin application of glaze will
never run, but it tends to cover the entire surface without any variety, and may
leave a surface texture feeling too raw. Between these two extremes, an
average thickness of glaze will deposit most heavily in recesses, moderate
thickness on flat surfaces, and thinnest on outer edges and corners. A colored
transparent glaze, such as a celadon, will always appear darker where it is
thicker, especially wherever there is a recess in the surface. Such a glaze, when
applied thickly, may completely eliminate the actual tactile qualities of the
original surface, but may retain considerable visual texture because of the
variations in glaze color in thick and thin areas. The classic Chinese celadons
are the prime example of this effect. When applied over a carved relief surface,
the celadon glaze tends to settle more thickly in the recessed areas, producing a
darker green accentuating the effects of light and shadow in a way that can be
very dramatic.
For heavily textured surfaces, glaze may be applied and then sponged off the
high spots. The piece can be fired like that, or it can be quick-dipped or
sprayed with the same glaze or a different glaze to bring back a thin glaze
coating on the high spots.
One of the most important and interesting glaze effects is color-breaking,
where a single glaze produces a variation in color dependent on glaze thickness
and the effects of oxidation and reduction. The most dramatic color breaking
always occurs in reduction high-firing. The classic East Asian brown-black
temmoku glaze is a perfect example. Most of the iron color we encounter in
rocks and in ceramics is red or ferric iron, which is the oxidized form of iron, as
in ordinary iron rust. But in a reducing atmosphere in the latter stages of the
firing, the iron in a temmoku glaze loses oxygen atoms and reduces to black
ferrous iron. Where the glaze is thick, it will permanently retain this black
coloring, because the molecules of black iron are impacted deep in the glass,
protected from re-oxidation. Once the kiln is shut off, all remaining carbon or
hydrogen in the kiln atmosphere immediately combust, and we are left with a
strongly oxidizing atmosphere. Anywhere the glaze is thin, the iron molecules
are exposed to this oxygen-rich atmosphere, and will return to the red ferric
form. So a temmoku glaze characteristically is black where thick, breaking to
brown or red-brown where thinner, usually on rims and outside corners and
edges. If a temmoku is applied too thin, the entire surface will re-oxidize to
red-brown. If the glaze is applied fairly thick overall and if there is no breakup
in surface relief, the entire piece might be pure black except for where the glaze
breaks to brown along the rim, and this can be very striking.
Similarly, in a well-managed reduction firing, a properly applied copper-red
glaze will develop a bright red color, and the color will be retained where the
glaze is thick, but will re-oxidize to a colorless transparent where it is thin. This
is especially striking on porcelain and white stoneware bodies, where the rims
and outside edges are white against a deep red.
Some of the most interesting glaze effects involve layering glazes and patinas,
and there are many ways to do this. A piece can be coated with a thin patina,
and wax resist decoration can be applied with a brush or sponge-stamp,
followed by an overall glaze coating. Where the wax decoration has been
applied, there will only be the patina on the bare clay. The same technique can
be used with multiple glazes. Decoration with wax resist can be brushed or
sponge-stamped over a raw glazed surface, and the piece can then be quickdipped into a second glaze.
Any glaze can be dipped, brushed, or sponge-stamped over another
glaze. Keep in mind the general guidelines for glaze applications and avoid
excessive buildup of glaze. Double dipping is rarely a good idea overall, unless
your glazes are adequately thinned and you do very quick dips. Spongestamped patterns are one of the most interesting ways to achieved rich layered
pattern effects at all firing temperatures.
Additional glazes can be brush-painted over a raw glaze coating, but the brush
will tend to drag unless the second glaze is thinned with water a bit. Use a soft,
watercolor brush with good reservoir capacity, and load it up with glaze. Use
quick, fluid strokes.
Glazes can be trailed and/or dripped over a raw glaze coating with a sliptrailing bulb. This can create very interesting effects, due to the additional
depth of glaze applied with the bulb, as compared to glazes brushed on a raw
glazed surface.
Underglaze Effects
Underglaze brush-painted pattern/imagery
Underglaze sponge-stamped pattern/imagery
Underglaze over resist (masking tape, stickers, latex)
Underglaze applied to relief surface and then sponged off high spots
Trailed underglaze
Oxide Stain/Ceramic Stain Patina Effects
Applied over relief surface, sponged off, high-fired without glaze
Applied over relief surface, sponged off, high-fired with glaze
Painted on dry raw glaze surface
Sponge-stamped pattern/design on raw glaze surface
Cuerda Seca
Glaze Effects
Glaze applied (sponge, pour, dip, brush, spray) to relief surface and
sponged off the high spots
Glaze applied (sponge, pour, dip, brush, spray) to a relief surface and
sponged off the high spots, and then quick-dipped in or sprayed with a
second glaze
Glaze design painted with brush over a raw glaze surface
Glaze surface variegation with wood-ash dusted over raw glaze on
rim/shoulder
Contrasting glazes spattered on raw glaze surface for visual texture
Glaze design sponge-stamped over a raw glaze surface
Glaze sgraffito cut through wax-coated glaze surface, exposing bare
clay
Glaze sgraffito cut through wax-coated glaze surface, with another
glaze dipped, brushed, or trailed over exposed clay
Glaze trailing over another glaze
Glaze applied (sponge, pour, dip, brush, spray) over resist with
masking tape or stickers
PARAPHRASED AND APPROPRIATED FROM Appalachian Center for Craft Homepage - Tennessee Tech Homepage
Site maintained by: Vince Pitelka - Last Updated: January 13, 2011
!
Possible Qualities of Ceramic Surface
Achromatic Deep
Gritty
Antiseptic Delicate
Grooved
Barren
Dimpled
Hard
Beaten
Dirty
Harmonious
Blistered
Drippy
Hostile
Pierced
Plain
Pock-marked
Polished
Polychromatic
Slick
Slimy
Slippery
Smooth
Soft
Blotchy
Boring
Bright
Brilliant
Bubbly
Bumpy
Burnished
Burnt
Busy
Cancerous
Carved
Chaotic
Cheap
Checkered
Cold
Complex
Cool
Cracked
Crackled
Cratered
Crystalline
Dark
Dry
Dull
Elegant
Eroded
Exciting
Faceted
Fat
Flat
Flecked
Flowing
Fluffy
Fractured
Freckled
Frothy
Funky
Fuzzy
Glassy
Glossy
Grained
Grainy
Greasy
Inviting
Iridescent
Light
Lively
Leathery
Loose
Lumpy
Luscious
Marbled
Metallic
Minimal
Monochromatic
Mossy
Mottled
Muted
Opalescent
Opaque
Opulent
Orderly
Pasty
Patterned
Perforated
Porous
Random
Reflective
Rhythmic
Ribbed
Rich
Rippled
Rocky
Rough
Runny
Rustic
Sandy
Satiny
Scaly
Scorched
Scraped
Shallow
Shiny
Simple
Silky
Slashed
Soothing
Spare
Sparkling
Speckled
Spiny
Spotted
Sticky
Stippled
Striated
Striped
Subtle
Textured
Tight
Translucent
Transparent
Velvety
Volcanic
Warm
Wavy
Waxy
Wet
PARAPHRASED AND APPROPRIATED FROM Appalachian Center for Craft Homepage - Tennessee Tech Homepage
Site maintained by: Vince Pitelka - Last Updated: January 13, 2011
The Content of Surface: Emotional and Psychological Impact
Every pattern, texture, and color communicates specific
psychological and emotional content, subject to individual
interpretation. It is essential to consider this when working with
surface decoration. Consider the words above and the possible
narrative content they carry. Consider the full range of color and
value - light and dark, cool, warm, and hot. Think about the
implications of various color combinations. Certain ones seem
discordant and disturbing, while others are soothing and
harmonious. Color is a very powerful tool, and it is the
responsibility of every artist to fully consider the narrative
implications of colors individually and in combinations.
Visual and actual texture can convey a wide range of
meaning. Visual texture refers to the appearance of texture,
regardless of the actual textural qualities when we touch the
piece. Many glazes appear very textural and yet are absolutely
smooth. Actual texture involves tactile sensation when we feel
texture on the surface of a piece. To imagine the emotional and
psychological associations with texture, we have only to think of
the words in the list above which have specific textural
associations - smooth, silky, greasy, hard, cratered, soft, fluffy
When we seriously consider the power and possibility of color,
pattern, and texture, we begin to appreciate the unlimited range of
content and meaning that can be communicated in ceramic
surface. As we explore surface design, consider these issues
carefully, and select your surface qualities deliberately according
to the narrative qualities you want to communicate. Be prepared to
talk about your choices.
PARAPHRASED AND APPROPRIATED FROM Appalachian Center for Craft Homepage - Tennessee Tech Homepage
Site maintained by: Vince Pitelka - Last Updated: January 13, 2011
Stages in Surface Development
Wet Clay - poke, push, prod, scrape, stretch, slash, groove, mold, model, incise,
impress. add, subtract, impress, flute, facet, slip-paint.
Leather Hard - carve, impress, stamp, applique, sprig, flute, facet, engrave,
add, subtract, scrape, mishima, inlay colored clay, laminate colored clay, slippaint, slip-trail, slip-layer, feather-comb, slip-marble, textured slip, slip-resist.
Bone Dry - carve, scrape, sand, sand-blast, slip-paint, terra sigillata, polish,
burnish, underglazes, green-glaze.
Bisque-fired - sand, sandblast, grind, engobes, underglazes, stains, glazes,
brush, dip, pour, spray, spatter, speckle, glaze-resist.
Glaze-Firing Processes with Varying Surface Effects - low-fire, mid-range,
high-fire, oxidation, reduction, sawdust-smoking, raku, bonfire, salt, soda,
sagger, wood.
Multi-firing Processes - enamels/china paints, lusters, decals.
After the Firing - sandblast, sand, grind, chip, break, reassemble, paint,
spackle, bondo, putty, mixed media.
!
PARAPHRASED AND APPROPRIATED FROM Appalachian Center for Craft Homepage - Tennessee Tech Homepage
Site maintained by: Vince Pitelka - Last Updated: January 13, 2011
ABSTRACTION…REALISM….NATuRALISM>>..ISM ISM!
Realism vs. Abstraction: Some Things to Consider
The following quotes are from Art Fundamentals, Theory and Practice,
Ocvirk, Bone, Stinson, & Wigg
It is interesting that the wholly abstract quality of music is so easily accepted,
but art as abstraction (except as pure ornamentation, as in wallpaper) is more
difficult to accept.
Abstraction is simply a matter of alteration and reshuffling of priorities in order
to convey the artist’s intent and/or feelings more effectively.
Genuine art does not limit itself to superficial appearances, but tries to reveal
that which lies deeper. It takes delight in pure invention and adventure.
There is very little excuse for judging a work of art solely on the basis of visual
accuracy.
It is possible to develop vision that looks through the encrustations of fashion
and fad, into the underlying formal structure.
Art is not primarily intended to be informative. Information is the province of
symbols such as words in literature or numbers in math. Art is primarily
experiential.
Artists are under no obligation to narrate (tell a story).
Art that places chief emphasis on accuracy of description is repetitive rather
than creative.
When students understand that art does not function primarily to describe
things naturalistically, their chances of realizing their own artistic goals will be
more closely realized. The formal devices of design soon become instinctive
tools of expression, giving the ability to conceive or imagine form in an
original way.
A painting or sculpture can be thought of as the record or expression of an
artists experience, from the age and place in which the artist lives.
The subject (of a work of art) is merely the stimulus to creativity.
Public vision is unfortunately often conditioned to be object-minded, satisfied
only with art that has an obvious basis of recognition.
The observer must learn to look for the expression of a work of art rather than
just the recognizable associations.
The Issue of Abstraction: Some Things Consider
"Reality has always been far too small for the human imagination." Jacqueline Ford Morie
Throughout history around the world most artwork has freely expressed the
wonderful potential of human imagination, using abstraction and symbolism to
empower specific narratives. In our Western culture the Classical humanism of
ancient Greece and Rome celebrated the idealized perfection of the human
form, and encouraged pictorial realism in all art . When many people think of
“art” they imagine the glorious paintings and sculpture of Renaissance Europe,
which can sometimes make it difficult for individuals to consider non
representational or abstract work as authentic “art”.
Abstraction in art can simply be defined as the alteration or interpretation of a
subject to suit the artists needs or intent, and under that definition almost all art
is abstracted from reality to some extent. The copying of reality without
interpretation or abstraction is a matter of rendering skill and involves little
creativity or imagination.
Nonobjective abstraction refers to completely abstract artworks with no overall
objective or recognizable content. This type of artwork demands a lot from the
viewer. When we view pictorial realism in art our response can be completely
passive. All we have to do is stand there and let the imagery deliver its
message, which doesn’t require much imagination or initiative on our
part. This is not to malign realistic pictorial art, but our enjoyment and
understanding of realistic imagery depend on the artist’s rendering skill and our
familiarity with the pictorial information, rather than our willingness to actively
use our intellect and imagination. Abstract art is appreciated on a different
level, and places much more responsibility on the viewer in order to actively
experience the work. The appreciation of abstract art can increase with
education and experience, but neither are necessary. The minimum
requirement is a keen eye and an open mind.
A comparison with music can clarify all this. Non-objective abstraction in
visual art is like instrumental music. To say that realistic pictorial art is
somehow more valid or effective than abstract art is just like saying that music
that tells a story with words is more acceptable than instrumental music. A
piece of instrumental music is an abstract composition of musical form: pitch,
tone, volume, duration, repetition, rhythm, unity and variety experienced
through sound. A nonobjective artwork is an abstract composition of visual
form: line, shape, volume, space, value, color, pattern, texture, repetition,
rhythm, unity and variety experienced through sight.