Porcelain Slump Mold Slip Glaze
Your Mission: Create a bowl using a mold with porcelain clay. Then using slip glazing, carve a design into the glaze using the scraffitto technique.
Vocabulary: porcelain, slump mold, slip glaze, scraffitto, bisque, clay, green ware, joining, kiln, modeling, pinch, score, slip, stick, wedging
Materials: Porcelain Clay, different tools for texture and scoring and slip, slip glaze.
Phase 1 - Planning
- Porcelain is generally believed to have originated in China. Although proto-porcelain wares exist dating from the Shang Dynasty, by the Eastern Han Dynasty (100-200 CE) high firing glazed ceramic wares had developed into porcelain, and porcelain manufactured during the Tang Dynasty period (618–906) was exported to the Islamic world where it was highly prized
- Chinese porcelain, which arrived in Europe before the 14th century, was much admired and expensive to purchase. Attempts were made to imitate it from the 15th century onwards but its composition was little understood. Its translucency suggested that glass might be an ingredient, so many experiments combined clay with powdered glass (frit), including the porcelain made in Florence in the late 16th century under the patronage of the Medicis. In Venice there were experiments supposedly using opaque glass alone.
- Bone china is a type of porcelain body first developed in Britain in which calcined cattle bone (bone ash) is a major component. It is characterised by high whiteness, translucency and strength. Production usually involves a two stage firing where the first, bisque, is without a glaze at 1280 °C (2336 °F), which gives a translucent product and then glaze, or glost, fired at a lower temperature below 1080 °C (1976 °F)
- Brainstorm & Draw
- 5-6 well developed drawings exploring incised designs for your bowl interior.
- Demonstration: How to use a slump mold
Dimensions & Requirements:
- 1 slab slump mold bowl
- Hand built techniques; slab
- A foot that enhances your form, lifts it above the flat surface and stabilizes the form
- Form is completed in slip glaze with an incised design that enhances your form
Phase 2 - Construction
- Get porcelain clay
- Wedge clay
- Begin by making a slab using the slab roller
- You must use a cloth or pillowcase to protect your porcelain from the other types of clay.
- Your tools must always be washed and cleaned of other clay debris before using them on the porcelain clay
- Place the slab over the mold and cut the excess clay off along the bottom of the mold
- Carefully smooth out the clay along the mold, causing the clay to take the shape of the mold.
- Let clay dry to a more leather hard state.
- Attach a foot that brings out the shape of the mold
- Demonstration: Using slip glaze
- Using the slip glaze paint the inside of the bowl.
- Practice incising your design in another piece of clay.
- Once the glaze is dry, you will carve out the planned drawing you have come up with in your sketchbooks.
- Make sure your name and date are on the bottom
- Place the finished sculpture in the kiln room to dry out for firing.
- Once fired you will need to glaze it with a coat of clear glaze to render the bowl usable.
• Clay must remain moist during construction
• Walls must be even in thickness - no more than ¼ inch thickness
• Interior of bowl is smooth
• Seams are smooth and invisible where necessary
• Foot is stable, well attached and supports the form
• Bowl stays together in “bone” dry state
• All crumbs and bumps are removed
CERAMICS II - CRITERIA FOR PORCELAIN SLUMP MOLD
Communication and Expression
- Clay is properly molded, and not mixed with other types of clay
- Sketch out designs for incising in the slip glaze.
Design and Composition
- Foot that enhances your form, lifts it above the flat surface and stabilizes the form
- Form is completed in glaze that enhances your form with incised design into the bowl
Methods, Tools, and Techniques
- Proper use of all clay tools
- Clay remains moist during construction
-Walls are even; ¼ inch thick
-Seams are smooth and invisible where necessary
-Base is stable and flat
-Structure stays together in “bone” dry state
-All crumbs and bumps are removed
-Name/logo on bottom of structure
Critique and Reflection
- Contributes to all group critiques in thoughtful manner
- Complete all written work and assessments
- Stays focused and on task
- Completes all work
- Adheres to deadlines
- Care & respect for all clay materials
- Appropriate behavior in Ceramic’s room
Slip Glaze Notes
You can use a slip tracer to draw with liquid clay slip. You can color the clay slip with colorants like red iron oxide (for browns) or cobalt ( for blues) or chromium oxide (for greens) etc. Add some water and a little glycerin to you clay, add 1 to 5 % of colorant ( commercial glaze stains work well too) strain it through a screen to remove some of the sand and grog that might be in your clay.
You can brush it on and scraffitto (draw by removing some of the slip...as the the Greeks did with attic pottery and terra sigilata) or use a slip tracer.....just a rubber bulb with a fine pointed end ( like the ones you can buy at a drug store for cleaning out babies noses...) just squeeze the bulb, put it into the slip and suck some slip up...then apply while gently squeezing the bulb to force the slip out. It will take some practice....I used to practice on newspaper....but applying to a rounded surface of a thrown form is more difficult. If you make a mistake, 'erase' with a knife blade.