HANDBUILDING - FALL, SEPTEMBER-OCTOBER 18, 2023

October 18, 2023
All of your works have been bisque fired. We were introduced to Surface Decoration last week with Underglazed. We used two strategies with this: newspaper resist and applicatio of tissue prints. The next stage will be to apply a clear glaze. For this class, we use Duncan Pure Brilliance which we fire to cone 05 (low fire).

We learned how to make underglazes by using a slip recipe with added colorants.

Strategies for Decorating the Surface of your Green ware using slips, underglazes and stamps

Slips and Stains

Hand built forms in clay include a mix of surface decoration which might include commercial underglazes, slips, stains and glazes. When considering colour and surface decoration, the word “slip” refers to a recipe based medium for a colorants. People working with clay commonly refer to slip and understand the word as a liquefied suspension of clay particles in water which occurs whenever one works with clay. There is also “slip-casting” which is also a recipe-based concept and used with molds.

Often handbuilt forms in clay include a mix of surface decoration which might include commercial underglazes, slips, stains and glazes (often just a clear glossy or matte). When considering colour and surface decoration, the word “slip” refers to a recipe based medium for a colorants. People working with clay commonly refer to slip and understand the word as a liquefied suspension of clay particles in water which occurs whenever one works with clay. There is also “slip-casting” which is also a recipe-based concept and used with molds.

Slips are applied to wet or soft leather-hard greenware. Slip used on bisque usually follows an engobe recipe. They can be washed away to create a weathered look.

 

Slips are applied to wet or soft leather-hard greenware. Slip used on bisque usually follows an engobe recipe. They can be washed away to create a weathered look.

 

Susan Feagin  (Cone 04-9) Custer Feldspar  27 EP Kaolin 34 OM4 Ball Clay 20 Sikica  19 -------- Zircopax  5

Sunshine Cobb Base Slip Cone 04-9 Kaolin  34 Ball Clay  20 Potash Feldspar  27 Flint-silica  19 Zircopax  8 Soda ash  0.25 Sodium Silicate  0.25 ____________________

Robin Hopper: WHITE BASE Cone 04-12 in Ceramic Spectrum): Ball clay 75 Kaolin 10 Silica 10 Feldspar 5

Colorants are added to the slips. There are two categories 1) Minerals 2) Mason Stains.
 I. Common minerals: Rutile (tan); Cobalt carbonate (blue – 1-3%); Iron Oxide (red-up to 15%); Copper Carbonate (green – up to 10%); chrome (darker green 1-3%).
2. Mason stains: infinite

Replace Underglazes with Engobes on Bisque Ware
Engobe recipe R Hopper –

Raw Material

Cone 04-3

Cone 4-6

Cone 6-10

Kaolin	20	15	15
Calcined Kaolin	10	20	35
Talc	25	10	5
Calcium Borate (or Frit 3110)	15	10	0
Nepheline Syenite	0	10	15
Silica	15	20	15
Borax	5	5	5
Zircopax	10	10	10
Total

 

Class Pictures are coming

Final Glazed Pieces

 

Many of our class works received a glaze coating inside and out. Everyone made their own choices as to clear, or colour, or white as well as, glossy or matte. Some moving glazes like floating blue and green sand produced some lovely colour. Also notice the moving blue stripes on the casserole dish; this was not planned but happened because the blue had additional flux in it (why we need cookies). It was a happy accident and worth pursuing further. Terrific job everyone - so lovely!!!

Left  -Floating Blue breaking over edges          Right - Tissue print over stripped Underglaze background

A clear can become cloudy if applied too thickly and/or a recipe. Top right is Tony's Clear over Underglazes which is generally fine but not quite right over black. 

             Above: Glaze: Green Sand - the close up show how it breaks to beige on the edges and foamy white green

                   Above: Clear over Underglaze & Tissue Print   Above: Floating blue on different textured grounds
 

     Above: vase (left) clear over Underglaze      Above center back: Clear over Underglaze & White Liner, front: floating blue

                        Some of our finished pieces. Glazes include Floating blue, Green Sand, Tony's White

These are painted with underglazes and given a clear glaze overtop (Tony's Clear). Inside: Tony's White.

Test tiles for sgrafitto and Mishima (These were fired with a Midfire clear - cone 6 - do you notice any difference in the brightness of the colours from above and below samples?)

These were painted and stained with underglazes and low fired (bisque - cone 05).  A lowfire clear glaze (Duncans Pure Brilliance - cone 05) applied as final coat. Lowfire firings (cone 06,05,04) with low fire clears maintain their bright colours.

 April 1, 2023 - ORPG Handbuilding Pictures of Processes

    Basic strategy for making a box                        Piercings & Correct Clay Stage (tool: exacto blade)


    Piercings: tool: hole maker            

 
                                                                              Building strategies: Coil and slab

    Coil & Slab: Intermediate

 
     Using our own stamps                                     Stage I decoration: Underglazes

  
Underglaze and tissue prints                         Underglaze: vintage look and wiping away

    Underglaze: Handpainted decoration

What is a glaze and How to use them??        Guild Glazes

                   Above:  Bisque Cart: these are ready for glazing - Glazes must be stirred each usuage

                Above: Liner glaze poured out                 Bottoms are sponged off                 What colour for the interior?

 

                        Applying resist to a glazed piece             Next: Our glazed and fired pieces
                                                                 

 March 30, 2023 - Glazes and Glazing

Last week we introduced glazes so that this week we could finish our work. This discussion will continue below (II).

I. Underglazes and "Low fire firings" (Temperature range cone 06, 05, 04)
In the last few weeks, we used Underglazes because of the wide range of colours available as well as, decorative techniques like sgrafitto and mishima. Our initial coloured test plates and tiles were fired (bisque fire:cone 05); touch ups were made and they were refired with a clear glossy glaze (1 coat of Duncan Pure Brilliance) and fired again (cone 05 - here we are not actually doing a "bisque" since the clay has already been vitrified but we are keeping the same low fire temperature because our glaze Duncan Pure Brilliance is made for low fire as per direction on the bottle. Many potters choose to do all of their work in low fire because of the colour brilliance  and Greener Environmental concerns.

II. Midfire Glazing (Temperature range cone 5, 6)
At the guild we do midfire cone 6 glazing. We discussed how glazes are essentially fluid glass once heated to the right temperature. A glaze is composed of three basic parts: glass, a flux (controls melt) and stabilizer (clay: controls drip).

These glazes are applied mainly by dipping into the bucket or pouring. Generally the rule is no thicker than a dime. The glaze must be well stirred before use and check with your finger that you see you nail as demonstrated in class,

       Above: ORPG Glazes - 2-3 greens, 2 blues, matte purple, tan, brown-red

What is a Glaze?

Glaze: glass + stabiliser + melter Glass: silica/flint/quartz Stabilizer: clay (alumina) Melter: Flux in feldspars

Glass formers

SiO2 - Silica - our main glass former

Al2O3 - Alumina - a very high temp glass former and glaze stiffener

B2O3 - Boron - low temp glass former (Gerstley Borate; ferro frits: 3124; 3134; 3110; 3195)

Clays (stabilizer) – keeps the glaze in suspension
● EPK (Edgar Plastic Kaolin) Al2O3 + SiO2
● Grolleg kaolin (china clay)
● OM4 Ball clay
● Red Art clay
● Bentonite - a powerful suspending agent

Primary fluxes (R2O) - get the melting started
    Primary Fluxes                                                                          Sources

Li2O - Lithium Na2O - Sodium K2O - Potassium ‘

Lithium Carbonate Nepheline Syenite Custer Feldspar Spodumene Cornwall stone Soda Ash

Secondary Fluxes (RO) - keep the melting going     Sources (RO)

MgO - Magnesium CaO - Calcium SrO - Strontium BaO - Barium ZnO - Zinc

● Whiting (calcium carbonate) CaO ● Wollastonite (calcium silicate) CaO, SiO2 ● Talc (magnesium silicate) MgO, SiO2 ● Dolomite CaO, MgO ● Magnesium carbonate MgO ● Zinc Oxide ZnO ● Strontium carbonate SrO ● Barium carbonate BaO ● Bone ash (tri-calcium phosphate) CaO, P2O

 

March 16, 2023 - Surface Decoration- Sgrafitti and Mishima

 This week, we consider a few decorative strategies using slips and underglazes. These strategies are used on green ware (or unfired clay).

Artists Shown in Class

Nancy Meiditz - her sgrafitto lines are bold and not likely done by a pin tool but a specialized carving tool (see Diamondcore for example).

                   Above: Janet DeBoos (sgrafitto on black underglaze and on terra sigilatta. Also uses decals                     which are applied after the glaze firing at 015- 018).

Above: Susan Feagin layers on many techniques including sgrafitto and mishima, but also newsprint transfers and more. Look her up on UTube.

Above: Adero Willard layers many areas of texture and colour. Foe example the light blue background with squares and arabesques are done using the mishima technique. Other areas are painted and wax resisted. Her strategies are discussed in Pottery Illustrated.

Techniques shown in Class Demos:

Class technique 1: Sgrafitto
The geometric patterns are drawn onto black underglaze (3 - 4 coats). If the clay is white, the incised lines are white. Note the great balance of black areas and the various widths of lines (several engraving tools).

Class Technique 2: Mishima 

This is done by scratching a design into the wax. When the wax dries, a black underglaze is applied into the lines. Allow it to dry and scrape or sponge off. Do not let the wax dry more than 30 minutes otherwise the lines donèt get through the wax.

In this picture (above) the wax has been applied & the design is drawn with an Exacto. I find it easier to do my initial drawing in pencil on the bisque, then cover with wax - this allows me to see the drawing as I cut through.

Above: The black underglaze was applied to the drawing. Each of three coats was allowed to dry before the next application. A sponge is used to clean up the surface but a scraper can also be used (the latter is the traditional Korean approach).

Various coloured underglazes are applied to the shapes.

About Slips.... 

Because we are still working with greenware objects, we are decorating with underglazes and slips which are structurally similar to one another.

Slips are applied leather-hard or bone dry greenware. However, the slip used on bisque usually follows an engobe recipe (see below). 

The example used in class for pure slip decoration was a cup by David Miller (UK). He often uses a white base slip and then adds further layers of coloured slips. I remember him saying once - "what you see is what you get.." referring to the mason stains added to a slip. (Try it out: place 3 tbs of white slip in a small container. Choose a mason stain colour and start with 1/2 a teaspoon on your lid, spritz and mix then add to the slip. Continue doing this til you reach your desired colour.

Above: David Miller Slip-based decoration

Comparison of a Basic Slip Recipe - Any Similarities?

Susan Feagin - White Base Slip  (Cone 04-9) Custer Feldspar  27 EP Kaolin 34 OM4 Ball Clay 20 Silica  19 -------- Zircopax  5

Sunshine Cobb Base Slip Cone 04-9 Kaolin  34 Ball Clay  20 Potash Feldspar  27 Flint-silica  19 Zircopax  8 Soda ash  0.25 Sodium Silicate  0.25 ____________________

Robin Hopper: White Base Slip Cone 04-12 in Ceramic Spectrum): Ball clay 75 Kaolin 10 Silica 10 Feldspar 5

Colorants are added to the slips. There are two categories:
1) Minerals/oxides 2) Mason Stains.

 I. Common minerals/oxides:  Rutile (tan); Cobalt carbonate (blue – 1-3%); Iron Oxide (red-up to 15%); Copper Carbonate (green – up to 10%); chrome (darker green 1-3%). These are available at the guild.

 2. Mason stains: infinite - These are available at the guild.

Slip-Engobe for a bisqued surface

Replace base slip with Engobes on Bisque Ware

Engobe recipe R Hopper :

Raw Material

Cone 04-3

Cone 4-6

Cone 6-10

Kaolin	20	15	15
Calcined Kaolin	10	20	35
Talc	25	10	5
Calcium Borate (or Frit 3110)	15	10	0
Nepheline Syenite	0	10	15
Silica	15	20	15
Borax	5	5	5
Zircopax	10	10	10
Total

 
Popular Request: Crack Mending (paper clay slip)

3 Tbs powdered clay (let scraps dry out and crush in a plastic bag)
6 squares of toilet paper (pull apart to 1 ply) torn into small bits
2-3 Tbs Water
1 drop of Darvan 7

Directions
Place drop of Darvan 7 in 2 Tbs of Water
Break up toilet paper and let disintegrate  in water
Mix powdered clay a bit at a time til disired consistency for filling in cracks