Thursday, March 30, 2023

 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
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


Friday, March 17, 2023

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





Calcined Kaolin








Calcium Borate (or Frit 3110)




Nepheline Syenite




















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

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

Saturday, March 11, 2023


March 11, 2023

This week we return to our Darted piece and consider our options for surface decoration. We will continue making our texture stamps. We will add decorative handles and sprigg molds using our magic slip (darvan 7 in the mix) to our darted piece. Next we will look at how to apply Underglaze paint and Underglaze slips. Linda will do a demo on how to make an Underglaze slip following this recipe:

Slip for Underglaze Painting 04-9
Susan Feagin

Custer Feldspar  27
EPKaolin     34
OM4 Clay    20
Silica    19
Add Zircopax  5

Mason stain 6129  6%
Rutile 2%
Yellow Green: Copper Carb  5%
Mason stain Yellow 6404

Class Demo:
2 Mason Stains  are chosen by class


                                           Artist: Susan Feagin who currently teaches at Penland

Strategies for Underglaze Painting

  Nancy Meiditz  (above)
Adero Willard (below)



Thursday, February 23, 2023

February 23, 2023
First Class

These are some of the topics that are discussed in the first class and placed here as a reference for your future work:

Preparing the Clay - Wedging
Each person ceives a half bag of clay. With the wire cutting tool, a demonstrated amount of clay is cut away with this too, Carefully keep bag closed to airtight. The cut away part of clay needs to be wedged.

For a review wedging 

Key Tools for Handbuilding  Wire Cutting Tool: This is used for cutting large amounts of clay or taking a form off the wheel. Rib: For smoothing out surfaces. These come in metal and plastic. Scoring Tool: This roughens up the clay for when two pieces are put together. It can be as simple as a fork or toothbrush. Smooth clay does not stick properly to another piece of smooth clay.

Brushes: Bristle (round and flat), Flat stiff (synthetic -1/2 in to 1in), soft (for painting - various sizes), fine point (example: Japanese or sable), Liner brush (long hair) and Fan brush (wide splayed, stiff)

Thursday, October 27, 2022

ORPG HANDBUILDING - FALL 2022 - General Outline for the Six Weeks


                                                                  Layering of Glazes

Waiting for the loading and firing
Glazed Class Projects
Preparing Samples: Based on one clear cone 6 base (Oxides: Cobalt, Chrome, Red Iron Oxide, Copper Carbonate, Rutile).

Colour Blends


Final Glaze Firing 
he class used several strategies for the final surface treatments of their projects. Some used the bright colours of underglazes along with a clear glaze. Others opted for the glazes available at the guild. Finally, some used commercial glazes. It really depended on their sensibilities and trying to materialize what is seen and felt by the maker.

Bisqued Plates and pots using transfer printing

Strategies for coil building
Week 6: Glaze Firing

Discussion: Firing  (electric, wood, atmospheric) and its effects. A PDF will be sent out on this.
Coil sculpture continued.
Everything but the coil project should be dry enough for firing. 

 In preparation for a glaze firing, you will be glazing some works in class. I have already bisqued many of your pieces so don't panic.
* We will be mainly using the clear glaze. This will be applied over your bisqued pieces by the pouring method.
* Other colours in the guild's glaze collection may also be used.
* Whatever is not finished for a glaze tonight, arrangements will have to be made with me for an extra session. 
* Some of you were asking about membership last week and this is the person to contact: Donna Schenher  - or check the website

* There will likely be another Handbuilding class starting around mid-February, so you may continue some work at this time. Let me know so that your name can go on a list for first announcements.

Week 5: Simple Glazing and Sealing
pdf has been sent out entitled "Glaze Info". We will be going through glaze theory that Thursday, Nov.3, 2022.
- key parts of a glaze
- decontructing glossy and matte; proportional relationships of silica to alumina
- colour additives: traditional oxides and Mason Stains
- what are encapsulated pigments
- a brief historical background to sealing clay (watertight to dishwasher safe).

Continue working on projects. 
Project: Transfer printed Plates - trim and add lip/feet - finish to dry.
New work: Start a coil sculpture/vessel on three legs (Candlabra or Tree of Life) - start by extruding coils and make a 3 part base lke a clover leaf.

Week 4: Transfer Printing onto a roundish/squarish plate (we are using Hump molds)

Above: Transfer Painting on Newsprint

Discussion: Draw out a simple design in the shape of your plate
Preparing the transfer: Using newsprint we will paint our design, cover it with slip and transfer this to the plate.
Technical: We will make coils on the extruder. These are added for a finer edge on plates. We will also use a coil to form a a foot on project 3 if its not too dry.
Drying: Tight wrap to looser wrap in week 2/3 - works from week 1 & 2 should be dry enough for firing (bisque fire).

White Slip for Transfer Process
Slips are very versatile and can be fired at almost any temperature. I am posting a few here that are very versatile:

All Purpose White Slip (Jason B Burnett, Pottery Mking, 2022 Sept/Oct.) Cone 04-10

Ferro Frit 3124  19.2%
EPK Kaolin  27%
OM4 Ball Clay  27%
Silica  21.$%
Zircopax  5.4%
= 100%
Add Mason stains up to 10%

Base Slip (Sunshine Cobb, Handbldg.)Cone 04-9

Kaolin  34%
Ball Clay  20%
Potash Feldspar 27%
Flint  19%
= 100%

   Zircopax  8%
Soda Ash  0.25%
Sodium Silicate  0.25%
Add Mason stains up to 10%

White Base Slip
(Robin Hopper, in Ceramic Spectrum) cone 04-12
Ball clay 75%
Kaolin 10%
Silica 10%
Feldspar 5%

(at cone 2 or lower it may cause the glaze to craze). 
Add Mason stains up to 10%

Week 3: Decorated Container - Moving Towards Complex Forms

Discussion: Using Darts to Alter the Form
A simple template design is given curves and movement through darting.Thinking of Surface Decoration from the start by impressing the surface with stamps, rollers, textyre plates. Adding textured cutout shapes over the base plane.
Technical: Demo on the slab roller usage.
Drying: Tight wrap to looser wrap in week 2/3.

Week 2: Tulippiere (Flower Vase) - Moving Towards Complex Forms

    Project: Tulippiere - Five Part Form

Discussion: Putting together multiple templates
The template as a deconstruction of various circles.
Our tulippiere: base, mug body (shortened a bit), shoulder, lip 
Thinking of Surface Decoration from the start: texturing of some parts before cutting of template, addition of spheres, slip dots and underglaze. Subtracting circles (using circular cutters) or geometric shapes.
Drying: Tight wrap to looser wrap in week 2/3

Week 1: Introduction
Week 1: Making a Mug 

Discussion: The Template
Where can we source a mug template and what is it based on?
Making Handles
Preparing the Clay - pounding, rolling, compressing & smoothing the surface
Clay readiness: soft slab and hard slab
Preparing for bisque firing: finishing details, cleaning surface, applying 3 Underglaze colours
Drying: Tight wrap to looser wrap in week 2/3