Slip Formulation & Deflocculation
Casting slip is not mere liquid clay; it is an engineered colloidal suspension stabilized by repulsive electrostatic charges. Unpack the chemistry of sodium silicate, polyacrylates, specific gravity verification, and thixotropic recovery.
Standard Stoneware & Porcelain Slip Batches
| Raw Mineral Constituent | High-Translucency Porcelain (%) | Cone 6 Vitrified Stoneware (%) | Functional Ceramic Role |
|---|---|---|---|
| Grolleg Kaolin / EPK | 50.0% | 28.0% | Primary refractory matrix, crystal formation |
| OM-4 Kentucky Ball Clay | 0.0% | 22.0% | Plasticity, green strength, colloidal suspension |
| 325-Mesh Potash Feldspar | 25.0% | 20.0% | Fluxing agent, primary eutectic melt initiator |
| Flint (Silica / Quartz 325#) | 25.0% | 26.0% | Thermal expansion controller, glass-former |
| Pyrophyllite / Talc | 0.0% | 4.0% | Thermal shock resistance, flux accelerator |
| Sodium Silicate (1:1.6 Ratio) | 0.15% (dry weight) | 0.22% (dry weight) | Electrolyte deflocculant (Na+ ions) |
| Darvan 7 (Sodium Polymethacrylate) | 0.10% (dry weight) | 0.08% (dry weight) | Organic steric dispersant, prevents hard-panning |
Colloidal Control Indicators
Specific Gravity Verification
Measure 100 ml of fluid slip on an analytical scale. Ideal ranges span 1.74 to 1.80 g/ml. Under-dense slip induces soft cast walls and prolonged drying; over-dense slip prevents capillary suction in plaster tooling.
Ford Cup #4 Flow Rate
Timed discharge of 100 ml slip through a standardized 4.12 mm orifice. Ideal initial effluence rate measures between 20 to 25 seconds. A slower time indicates under-deflocculation or premature thixotropy.
Thixotropic Gel Strength
Evaluating viscosity delta after 5 minutes of rest vs. agitated state. A controlled thixotropic structure holds heavy coarse grog in suspension while liquefying instantly under slight mechanical agitation.