Glazing and Firing
Name the fired stage of clay that has been through its first kiln firing, is hard but still porous, and is ready for glaze application.
BISQUE
Describe two common application methods for overglaze and one advantage of each.
Dipping (even coverage, efficient for multiple pieces); Brushing (control, detailed application).
What is the purpose of scoring when joining two pieces of clay?
To create a rough area for slip to key into so pieces bond securely.
State one fundamental functional difference between underglaze and overglaze.
Underglaze is applied before glazing (often before clear glaze) as color/design; overglaze is the glaze layer (melts into glass) applied typically after bisque.
Define a slab pot in studio ceramics terms.
A pot constructed from rolled slabs that are joined (slapped) together to form walls and base.
Explain why leaving a foot ring (unglazed bottom) is critical before a glaze firing.
Prevents glaze from sticking to kiln shelf during glaze firing; allows safe placement on shelf.
Why are test tiles recommended when experimenting with a new glaze and firing schedule?
Test tiles record color response, gloss, and fit at exact kiln schedule and clay body; reveal crazing, crawling, or interaction issues.
Describe the ideal consistency for slip used as a joining agent and how to test it.
Consistency: like heavy cream. Test: brush or drip should hold slightly and not run off; it should adhere when applied to a scored surface.
Why must underglaze often be sealed with a clear glaze to be food safe? Include the role of vitrification and permeability.
Underglaze pigments remain porous until sealed by a clear glaze and final glaze firing; without being vitrified by glaze, pigments can wear off and are not reliably food-safe.
Explain why guide sticks are used and demonstrate (in words) the correct rolling motion to achieve an even slab.
Guide sticks set slab thickness; roll outward from the center with even pressure, flip/rotate slab, and maintain roller contact on sticks for uniform thickness.
Define vitrification and describe its importance for functional ware.
clay body becomes non-porous and glass-like at sufficient temperatures, making ware stronger and potentially waterproof.
Explain why thin, even coats of glaze are recommended instead of heavy, single coats; include how this affects firing and the final surface.
Thick coats can run, trap gases, and cause uneven melting; thin coats allow controlled maturation and reduce defects.
When attaching a slab side to a curved form, what scoring pattern and joining technique improve bond strength and minimize cracking at the seam?
Use cross-hatched (criss-cross) deep scratches on both surfaces, apply generous slip, press and brace with ribs or supports, and smooth from inside/out with sponge to reduce stress concentrations.
Explain the procedural difference (sequence of firings and applications) when using underglaze versus overglaze on a mug decorated with detailed imagery.
Underglaze: apply to greenware or bisque (depending on product), then clear glaze and glaze fire. Overglaze: apply to bisque and glaze fire directly (no clear glaze required if it’s the only finish).
When cutting slab pieces with templates, why is it important to cut at a 90° angle, and what problem arises if edges are beveled instead?
A 90° cut produces straight vertical edges enabling flush joins with full contact area; beveled edges reduce surface contact, causing weak joints and gaps when assembling.
Compare Cone 05 and Cone 6 in terms of typical temperature and at least one practical implication for glaze choice.
Cone 05 ≈ 1800 °F (low-fire); Cone 6 ≈ 2200°F(mid-fire). Practical implication: color range and glaze compatibility differ; some glazes and clay bodies require higher temps to mature.
Outline a step-by-step protocol (3 steps) to safely prepare and apply clear glaze over an underglaze design so it remains detailed and food-safe.
Steps: ensure bisque cleanliness; apply 2–3 even coats of clear glaze (brushing or dipping) allowing dry time between coats; wipe foot ring; allow full dry time; know if the clear coat is high or low fire
Explain why scoring only the surface (shallow scratches) can lead to failed joins after firing, referencing clay body moisture content and mechanical interlock.
Shallow scratches don’t provide mechanical interlock; as moisture changes, joints can shear because slip cannot penetrate and bond; deeper, multidirectional scratches allow slip to key in.
A student wants bright, precise illustration on a plate that will be used for food. Recommend a workflow choosing underglaze and/or overglaze, justify choices, and note any studio precautions.
Recommend underglaze for precise imagery, then clear glossy glaze for food safety; precautions: ensure underglaze is fully dry, apply clear glaze in even coats, wipe foot ring, label and follow kiln schedule; test on tiles first.
Provide a stepwise method for storing cut slab pieces to preserve workable moisture for later assembly, including environmental controls and time guidelines.
Store flat, wrapped with plastic, maybe lightly mist occasionally; place on a flat board; avoid stacking heavy pieces; store at consistent room humidity; use same-day assembly within 24–72 hours depending on moisture.
Given a glaze that consistently crawls during firing on textured surfaces, list three possible causes and one corrective strategy for each cause.
Examples: (a) contamination (oil/dust) — clean and re-wipe; (b) improper glaze fit/chemistry — reformulate or use compatible glaze; (c) firing atmosphere/temperature ramp — adjust schedule or soak; (d) application too thick — thin coats or adjust application method.
A student reports pinholing (small dimples) in the glaze surface after firing. Identify four likely causes and a targeted remedy for each. Guess 2 answers correctly for credit.
Pinholing causes: rapid firing ; trapped organic matter (clean bisque thoroughly); over-thinned glaze (adjust viscosity); reaction with clay body (test different glaze/clay combos).
A leather-hard slab box cracked along a seam during drying. Provide a troubleshooting analysis listing at least four possible causes (material, technique, or drying), and propose corrective actions for each.
Causes & fixes: (a) uneven slab thickness — re-roll to consistent thickness; (b) insufficient slip or poor scoring — reattach with proper scoring/slip; (c) drying too fast — slow drying with plastic; (d) differing clay moisture — equalize moisture before joining.
Evaluate the technical reasons overglaze can “drip” during firing and propose three studio-level controls (materials, application, and firing schedule) to prevent it while maintaining glaze effect.
Overglaze drips due to excessive thickness, incorrect viscosity, or incompatible melting point. Controls: apply thinner coats; adjust glaze formulation/viscosity; modify firing ramp/soak to reduce surface tension flow; stilt where necessary.
A set of slab panels for a large box shows slight dimensional differences (warping) after drying. Propose a diagnostic checklist (5 items) and corrective studio practices to minimize future variance during rolling, cutting, and drying.
Diagnostic checklist: (1) uneven guide stick height; (2) inconsistent rolling pressure; (3) different clay conditioning/wedging; (4) environmental humidity or drying drafts; (5) handling or flipping tensions. Corrective practices: calibrate sticks, standardize wedging, control studio humidity, use consistent rolling technique, and allow slabs to relax under plastic before cutting.