7/27/2019 Ceramic Glazes 2ndEd http://slidepdf.com/reader/full/ceramic-glazes-2nded 1/16 getting the most out of ceramic glazes and underglazes using commercial ceramic glazes and underglazes to achieve color, depth, and complexity | Second Edition | This special report is brought to you with the support of Mayco ceramicarts dail y .org
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A World of Colorby David GambleUnderglazes are one o the most popular ways to add color to clay suraces. They’re easy to use, and underglaze colors
are pretty much a “what you see is what you get” kind o proposition—blue fres blue and orange fres orange. The
best part is that underglazes come in all orms like underglaze pens, underglaze pencils, underglaze crayons, and more.
Homemade Underglazesby Holly GoringUnderglazes are widely avaialble but i you’re adventurous, you may want to try to mix your own. Holly provides a basic
recipe and instructions or creating your own underglazes and the special instructions required or success.
Creating a Weathered Look
by Jeffrey NicholsJeery explains how he discovered a weathered surace eect using underglazes on his precision-made teapots.
Discover how he does it using underglazes and sandpaper and give it a try on your next pot.
Using Ceramic Underglazesby David L. GambleCommercial underglazes are a great way to add color to your work using a variety o application methods. They’re ormulated
to have low drying shrinkage, they can be applied to bone-dry greenware or to bisque-fred suraces. In addition to being
able to change the surace color o your clay body, underglazes can also be used to change the texture o the body.
Creating Depth with Ceramic Glazeby Lisa Bare-CulpThere are many ceramic glazes that look great all by themselves, but you can really bring your own style and voice orward
when you start using techniques like pouring, carving, and layering to create depth in the ceramic glaze surace.
Low-Fire Red GlazesBy David L. GambleI you have ever tried to ormulate a red glaze, you know how difcult it can be. But even i you buy commercial red
glazes, you understand that they need a certain amount o attention and precision paid to them during application and
fring. This article will help you understand and keep track o all the variables when applying and fring red ceramic glazes.
Getting the Most out of Ceramic Glazes and Underglazes Using Commercial Ceramic Glazes and Underglazesto Achieve Color, Depth, and ComplexityCeramic glazes and underglazes are varied and wondrous concoctions. Because they can be complex, as well as or
ease o use and time savings, most o us use commercial ceramic glazes to some extent. Chances are, even i you are aceramic glaze mixing master, you have a ew commercial ceramic glazes or underglazes around the studio or specifc pot-
tery applications. Maybe you want to rely on commercial glazes or your liner glaze, so you’re sure it will be ood sae, or
perhaps a commercial ceramic glaze provides that hard-to-ormulate color you need or details in your surace decoration.
Getting the Most out of Ceramic Glazes and Underglazes: Using Commercial Ceramic Glazes and Underglazes to
Achieve Color, Depth, and Complexity provides several approaches and techniques to successully identiying, applying
Standard Clay Underglaze 23 06–5Underglaze Painting Medium
quantities, and in dierent ormats, such as crayons, pencilsand pens. I you’re not sure what you’d like to do, order2 oz. bottles and experiment beore you invest in pints orgallons. Here is a partial listing o oerings, but rememberthat most o the companies listed here sell their productsthrough distributors. For more inormation, go to the com-pany websites or check with your local supplier.
Underglazes are oneo the most popular
ways to add color to claywork. They’re easy to useat any age or skill leveland they can be applied atboth the green and bisquestage o work. Underglaz-es come in many orms—liquid, powder, pencil,crayon, liquid writers, bot-tle applicators, underglazepads, watercolor-type pan
sets and tubes. Typically,liquid underglazes containgum or binders to help
them adhere to ware and also add some green strength.I you decide to purchase dry underglaze, you may alsoneed a mixing medium, or example, Standard Ceramicsspecies mixing one part colorant and one part mixingmedium. The medium adheres well and creates a hardersurace than water so there is less smearing i you’reworking on bisque and placing a clear glaze on topbeore ring.
Underglaze pencils, crayons and chalks vary depend-
ing on the manuacturer. They’re designed to be usedon bisqueware because rubbing them onto a ragilegreenware surace can break the greenware. Pencilsproduce a nice pastel or a pencil-type eect dependingon how smooth the clay surace is. Many are very dry
and break easily duringapplication, and most areimported rom outside theU.S. Some pencils containwaxes to help them adhereto a bisque surace, butthese need a clear glaze
on top to keep them romrubbing o ater they’rered. Caution: Never putunderglaze pencils in anelectric pencil sharpener.
Many companies oerunderglazes by dierentbrand names, but they allpretty much unction thesame way. Underglazescome as premixed liquidsor dry, large and small
Test all underglazes or yourstudio conditions—clay body,fring, overglazes, etc. Createtest tiles with samples andapply a clear overglaze to halthe swatch. You’ll fnd thecolors deepen in value with aclear glaze.
Underglazes are the mostversatile o products or theclay artist. Available in morethan 1000 colors, underglazes
come in both dry and liquidorm as well as pencils, cray-ons and chalk.
The truth is, I was a nerdy ceramics undergradu-ate student. I wanted to learn everything, right
away—and I loved my glaze calc class. No, re-
ally, I did. I took a ridiculous amount o notes and then
put them all in plastic sleeves in a binder. I’m sure I
tested every recipe I could nd or invent. Ater discov-
ering commercial underglaze, I was sure I could make
that too.
Smooth, silky, perectly opaque, commercial under-
glaze is that wonderul substance that coats and colors
both greenware and bisque ware with ease (I’ve even
seen it work on mature cone 04 earthenware), and
without faws. And, in terms o color, what you see
is what comes out o the kiln, no guessing, no hop-
ing. They are dependable as well; covering large areas
quickly with smooth and consistent brush painting.They take light-colored, transparent or clear glazevery well without dissolving into the glaze during
the ring. Finally, commercial underglaze res intoa hard, unscratchable surace without pinholing orfaking rom cone 04 all the way to cone 10.
Commercial UnderglazesToday, most commercial underglazes are ormulatedusing rits, which reduce shrinkage, allowing themto be applied to both greenware and bisqueware.They are produced using a colloidal process. A col-loid is a substance microscopically dispersed evenlythroughout another substance (think mayonnaiseor hand cream). Underglaze manuacturers use a
chemical process that employs a high-shear mixingtechnology to create colloids. The substance createddoes not settle and cannot be separated out by ordi-nary ltering or centriuging like those in a typicalsuspension. This allows or complete integration o all raw materials, including the colorant, during thebase mixing stage.
Underglaze applied over red earthenware. White slip was applied to hal o the test tile beore bisque fring. This is no-ticeable in the white, orange, and red tiles where the application was thinner. See recipe on next page.
Developing the RecipeVariations o underglaze recipes were available onthe Internet but not much could be ound in text-books, beyond iterations o slips (clay suspended inwater, ormulated to t either to wet or dry green-
ware) and engobes (generally a lower clay content,most oten ts greenware and bisque ware ). Few o these recipes encompassed all the characteristics Iwas looking or—something similar to commercialunderglaze. Not too much to ask, right?
I started by choosing a clay and a fux. I neededa airly heavy clay content or adhesion to the claybody, and an equal amount o fux to lower themelting point o the silica, and to create a hard sur-ace. My clay choices included: EPK kaolin, calcinedkaolin, OM-4 ball clay, and talc, all airly whitering as to not add to the color, and each contrib-
uting something dierent to the adhesion needed.My fuxes consisted o: Ferro rits 3124, 3134, and3195, a good place to start in terms o readily avail-able rits. Then in a radical move, I ignored all previ-ous instruction and treated the colorant as one o thebase ingredients. This allowed or ull incorporationo the color with the other two ingredients duringthe mixing o the base recipe. I used commercialstains in order to get an opaque quality (I later testedvariations with oxides that resulted in a somewhattransparent underglaze.)
I mixed 1000 gram batches in a thousand varia-
tions (or something close to that). I actually mixedthree batches o each recipe to test gums and sus-penders, without which, any substance mixed romthe above ingredients would settle to a rock-hardmess and be nearly impossible to brush onto anyclay surace. I tested CMC gum (powder, premixedinto a liquid), premixed bentonite, and Sta Flo laun-dry starch (a tip rom one o the internet recipes).
Not having the ability to replicate the colliodalprocess, I sieved and ball milled each recipe in orderto ully integrate the raw materials and to reduce theparticle sizes as much as possible.
I tested each glaze on leather-hard, bone-dry, andbisqued earthenware and stoneware test tiles. I redthe earthenware tests to cone 04 and the stonewaretests to cone 6 and cone 10, all in an electric kiln.
Ater many rings and many eliminations, thisrecipe came very close to replicating commercialunderglaze:
Holly’s UnderglazeCone 04–10
Ferro Frit 3124 333 %
EPK Kaolin 334
Commercial Stain 333100.0 %
Sieve all materials with an 80 mesh sieve and then ballmill for at least 12 hours. Incorporate Sta Flo LaundryStarch until the mixture reaches a thin yogurt consistencyand sieve the entire mixture again.
Pros and ConsThe results were good, very good—smooth,creamy, good adherence, versatile at all tempera-tures, a hard surace, and an intense color. Theunderglaze worked well on both clay bodies and inall stages, but was best on bisque ware. Brushabil-ity was best with the Sta Flo. I ound that too thicko an application caused faking and pinholing.The lack o sieving and ball milling did the same.I mixed to the correct consistency, one coat wassucient while two coats oten was too much. Thecolors became muted when red to cone 10 butstill held up in hardness and adhesion. Only smallbatches could be mixed at a time due to the inclu-sion o the Sta Flo, which is organic and causedmold to grow in the bucket within a ew days. Themold could be skimmed o but added unwantedlumps i it wasn’t all removed. And o course theamount o commercial stain used to produce therich colors similar to commercial underglazeswas ultimately very expensive. In the end, mixingthis homemade underglaze was a lot o work ora product the manuacturers do just a bit better,
aster, and cheaper. However, i I want colors thataren’t available commercially, now I know how tomake them.
You can also layer the underglazes by sponging them
on i you do not have access to a spray booth. I rec-
ommend wearing gloves i you take this approach.
Ater the underglazes have dried, I begin sanding
through the dierent layers exposing the other col-ors, as well as the earthenware clay body underneath.
Again, remember to wear a respirator! I start with
320-grit sandpaper working to a 600-grit surace. I
then re the piece to cone 04, holding it at matura-
tion or ten minutes to create a strong bond between
the clay body and the underglazes.
It is important to apply this surace only to the out-
side o vessels or in areas that do not come in contact
with ood or drink. When red, the Velvets and other
underglazes have the durability o a matt glaze, but
are not ood sae. I then apply a ood-sae liner glaze
to the parts that will come in contact with ood andre the vessel again.
Faceted tea bowl with our layers o underglazessprayed on then sanded o to reveal the layers, giv-ing the piece a weathered look. A black was appliedfrst ollowed by red, light blue then medium blue.
Faceted teacup and saucer with our layers o underglaze(black, red, yellow, and orange) applied then sanded. Anynumber o underglaze colors can be added in any combina-tion—the choice depends on the eect you’re looking or.
Nichols uses a respirator and a hooded exhaust vent tomanage the dust created when sanding his dry suraces.Below is a surace detail revealing the layers o colors.
When used to add color to sur-aces, underglazes have an advantage
in that they are composed mostly o
clay with very little fux, so they’ll
stay put and won’t run, which makes
them ideal or detailed decoration.
While most underglazes were origi-
nally ormulated or use at low-re
temperatures, most, maintain their
color in the mid range and some even
as high as cone 9 or 10.
Simple ApplicationUnderglazes can be applied by brush-ing, pouring, dipping, spraying,
sponging—pretty much anything
goes. Each application method has
dierent requirements. I an under-
glaze is too thick or spraying or
using as a wash, just add water to
thin it down. I it’s too thin or silk
screening or monoprinting, leave the
container exposed to air to evaporate
some o the liquid.
Underglazes work best with a clear
overglaze, although other glazes o
varying opacity and color may also
be used. I’ve had success with whites
and very light-colored glazes, but
darker glazes seem to muddy or ab-
sorb the color o the underglaze. The
overglaze can be anywhere rom matt
to glossy. You’ll nd the clear deep-
ens the value o the colors regard-
less o application method. I you’re
sealing the surace o work that will
“Teapots” by Jim Kemp. Jim uses a low-fre red clay body and airbrushes under-glazes onto the greenware. The last color he applies is black, which is sprayedacross the piece to highlight the variations in heights o the surace decoration.The pieces are once-fred to cone 02.
come in contact with ood, be sure to
use the appropriate ood-sae clear
that matches your clay body and r-
ing range.
Applying an overglaze can be
tricky. I you’ve applied underglazes
on bisque, you’ll nd that they’ll
smear when brushing on a clear over-
glaze because moist glaze moistens
the underglaze. Use a an brush and
foat the rst coat on without going
over the same area twice. Wait or
the rst coat to dry completely beorebrushing on a second coat.
I’ve recently used underglazes to
create a watercolor eect by thin-
ning them down and painting them
onto a semi-white glaze that is lay-
“3 Women Praying” by Debra Fritts.Debra sculpts in terra cotta clay andbisque fres to cone 02. She thencovers the piece with black stain andthen underglazes are applied, wipedand scraped, then fred to cone 04.She continues with fnal additionsand does a fnal fring at cone 05.