Archive for the ‘Techniques’ Category

17 PMpWed, 28 Apr 2010 23:31:59 +000031Wednesday 2010

SORRY – I have just seen my last entry with the recipes all oddly spaced. Not very helpful, so I am trying again just the recipes this time.

LITTLE SELECTION OF SLIPS FOR SALTGLAZE

Any oxide, or mixture of oxides, or any glaze or body stain (or their mixture) may be used in saltglaze slips, with interesting results.

Dry Oranges, Yellows and pinks

Try: Mixtures of various Ball clays and China Clay.

Good results – for example:

AT Ball Clay. 20

China Clay     80

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AK Ball Clay  40

China Clay     60

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SMD  Ball Clay   50

China Clay          50

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Porcelain          75

China Clay        25

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Fireclay         20

China Clay     80 (fierce orange)

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Porcelain Clay 20

China clay 10

Tin oxide 3

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Porcelain Clay 98

Illmenite 2

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Browns:

Shiny Brown: Red Clay  50

BBV Ball Clay 40

Flint 10

Experiment with Red Clay and China Clay mixtures + Iron oxide.

Pure White slip:

Hyplas 71 ball clay 25

China Clay       25

Flint 35

Cornish stone 15

Rich  Glossy or Fluid Oranges

AT Ball Clay 60

Potash Feldspar 20

Whiting 10

Flint 10

Rutile 10

Red Iron Oxide 5

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SMD Ball Clay 75

Grolleg 25

Vanadium Pentoxide 15

Titanium dioxide 10

Tin Oxide 10

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AT Ball Clay 63

Nepheline Syenite 32

Flint 5

Zirconium Silicate 5

Titanium dioxide 10

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Base slips for colorants to be added

China Clay              30

SMD ball clay         40

Flint                         15

Nepheline Syenite         15

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Nepheline syenite 50

Hyplas 71 Ball Clay 50

Colorants:

8% Rutile – pearl – tan

5% Titanium dioxide – pearl

0.5 %-3% Cobalt Carb. – blue

6% Rutile + 3% Cobalt – green

6% Manganese dioxide. – brown

!0% commercial stain can be added to the recipe

To encourage break up in salt glaze as used by Daniel Boyle

Vanadium Base slip

China Clay 55

Potash feldspar 25

Quartz 15

Bentonite 5

Vanadium Pentoxide 10

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Top slips

China Clay 17

Ball Clay 19

Flint 24

Nepheline Syenite 31

Standard Borax frit 9

Titanium Dioxide 9 for moonshine white

Or

Cobalt Carbonate 3 for blue

Raw Lining Glazes

Nepheline syentie 1

Soda Feldspar 1

AT Ball clay 1

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Nepheline syenite 33

AT Ball Clay 33

China Clay 33

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Potash feldspar 1

Cornish Stone 1

Hyplas 71 Ball clay 1

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I hope that this is clearer

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TECHNIQUES (notes by P.E. Maddalena)

17 PMpSat, 17 Apr 2010 21:31:51 +000031Saturday 2010

There are many different ways of using vapour glazing techniques. From the choice of the clay, slips and glazes, through the making and decoration processes, to the final glazing and firing alternatives. All of these choices are important for a personal statement and therefore the spectrum of possibilities is again limitless.

In order to have some basic view of the process I have restricted my exposition to three main ways of interpretation:

a) Soda firing. Basically derived from salt firing and its typical aesthetics.

b) Soda, Clay and Fire. A new intriguing and revolutionary approach.

c) Variations through soda. A much practiced way of using soda with glazed surfaces.

a) SODA FIRING (by P.E. Maddalena)

17 PMpSat, 17 Apr 2010 21:30:21 +000030Saturday 2010

Jane Hamlyn

Soda firing is done in a conventional way, often eliminating the biscuit stage. It makes the firing process slightly longer but in the end it saves in time and fuel.

Soda can be introduced in a variety of ways: spraying it dissolved in hot water, drip-feeding the solution, as small blocks of various compositions, etc.

The drip feeding is an excellent method since it only requires a short length of angled iron and achieves a good and even distribution of soda. Heavy build ups of soda obliterate colour in the yellow/orange variety and make some slips run.

As the solution breaks down in the heat of the flame, water vapour is released along with the vaporizing soda. Water vapour helps to carry the soda through the kiln chamber, enabling good glaze distribution and evidence of flame movement on the work. Water vapour also appears to assist with soda dissociation and glaze formation.

Firing cycle

The typical technique would be raw firing with pre-heating and slow raising temperature to take the clay through it’s biscuit process. If the work is already biscuit fired then, of course, the initial stage can be quite fast.

Walter Keeler

After soaking the kiln for about one hour at around 900°C, to burn out any carbonaceous matter to avoid any possible bloating, a reducing atmosphere is necessary to convert the ferric oxide compounds in the body and in slips to the ferrous state. Depending on the clay, often around 1150°C, it could be good practice to oxidise for a few minutes in order to avoid any carbon trapping when sodium already present in the kiln is beginning to vaporise and seal the body. Then maintain only a light reduction or neutral atmosphere throughout the rest of the firing.

Soda starts to be introduced into the kiln at cone 8 through cone 10.

The use of test rings is necessary to understand how the glaze is building up.

An oxidation soak of about an hour at the end of the firing will give warmer oranges from iron bearing bodies and slips.

The kiln is then crash cooled down to about 950°C.

Ruthanne Tudball

Ruthanne Tudball is one of the foremost ceramic artist investigating and using soda vapour glazing. She has written a book “Soda Glazing” edited by A&C Black . London and first published in 1995.

b) SODA, CLAYS AND FIRE (by P.E. Maddalena)

17 PMpSat, 17 Apr 2010 21:29:59 +000029Saturday 2010

Gay Nichols

Gail Nichols is a potter whose technical research and artistic approach to soda firing has literally opened up new aesthetics in the world of ceramics.

In contrast with the general rule of using high contents of silica in the clay, she uses high alumina clay bodies which reacts to soda vapour to create a generous opaque glaze, dimpled and frosty matt, giving the impression of glacially flowing ice.

It bears little resemblance to traditional salt glaze, or to the bright glassier styles of soda glaze. Unlike slips or detailed surface marking of much salt and soda glaze work, this very special technique tries to focus toward another aesthetic in which the thickly formed glaze flows over, interacts with and softens the form.

Fairly slow cooling is required to create frosty mattness (two hours to 1100 °C and three more to 800 °C). It was also discovered that water vapour in the kiln can alter the glaze colour and increase the crystalline mattness. Compounds like calcia, magnesia, silica, iron or wood ash are to be avoided.

Firing cycle

After reaching 900°C start reducing and fire up with light to medium reduction.

Soda introductions begins at cone 8 with intervals of about 15 minutes with temperature raising up to cone 9 and 10 down.

At cone 10 maintain temperature for two hours (cone 11 down) then fire down to 1000 °C in two hours and again cool down normally to 800 °C in three hours.

Gay Nichols

Considerations

In Gail Nichols experiments, the soda “ice” glaze formed most successfully in oxidation. Its maturity and colour were enhanced by reducing during the first cooling stage. When reduced cooling below 1000 °C, the colours became muted, producing dull browns instead of reds and oranges.

Reduction during the high temperature glaze forming stages produced some strong colours with close resemblance to traditional salt glaze. Shino style slips and glazes also developed much stronger colour when exposed to this reduction.

It seems that for colour enhancement during cooling, water vapour is most effective between 1000 °C and 800 °C. Water during cooling can also be used to create matt glazes from otherwise glassy surfaces.

Copper and manganese pigments blend well with soda “ice” glaze.

Strong red colours are assisted by a reducing atmosphere and water introduction during glaze forming stages, as well as by reduction during the early stage of cooling.

The “ice” glaze owes its opacity and mattness to a complex mixture of surface distortion and crystallisation. Its icy character is caused by its high soda content, the complete absence of other fluxes, its low silica/alumina ratio, and the absence of crystallised iron. The best ice glaze seems to be obtained in oxidation.

Gay Nichols

Gail Nichols has written a book, “Soda, Clay and Fire” on her distinctive approach to soda vapour glazing published by The American Ceramic Society in 2006.

c) VARIATIONS THROUGH SODA (P.E. MADDALENA)

17 PMpSat, 17 Apr 2010 21:28:51 +000028Saturday 2010

Peter Meanley, Pietro Maddalena, John Chalke.

Soda is a flux and on its way to the chimney will attack and change both in texture and colour any ceramic surface, clay, slip or glaze. Many potters exploit this fact and choose to benefit from it at different temperatures and intensities.

One very good use of the process, altering also temperature and firing schedule, is to soda fire lightly over a selection of otherwise normal stoneware glazes. This firing technique will give the work that extra richness of surface and colour that can enhance further the making process.