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Most jewelry investment powders use a 2.5:1 to 3:1 powder-to-water ratio by weight. Always follow the manufacturer's specification on the bag — ratios vary by binder type (gypsum vs phosphate-bonded).
Water (g) = Investment Powder (g) / mix_ratioCalculate the cylindrical volume of the flask minus wax tree displacement. Add 10–15% extra for spillage and bowl coating.
Volume = π × (diameter/2)² × height − wax_displacementMixed slurry density is approximately 1.9–2.1 g/cm³. Convert flask volume to required powder weight using the mix ratio.
Powder (g) = flask_volume_cm³ × slurry_density × (ratio / (ratio + 1))Updated: July 2026
A typical jewelry flask 3 inches diameter by 4 inches tall with moderate wax tree.
→ Investment powder: ~680 g; water: ~247 g; mix to 18–20 sec vacuum
A 4×6 inch flask casting 8 rings on a sprue tree.
→ Investment powder: ~1,450 g; water: ~483 g
A 2×2.5 inch flask for a delicate pendant with thin sections.
→ Powder: ~220 g; water: ~88 g; use 8-minute working time
Always weigh both components. Powder density varies with humidity and settling; volume measurements produce inconsistent slurry viscosity.
Use room-temperature distilled water (68–72°F). Warm water accelerates set time; cold water extends it unpredictably and can cause stratification.
Vacuum mix for 90–120 seconds to remove air bubbles that cause surface defects (gas porosity) on castings. Vacuum the flask again after pouring.
Lost wax casting requires precise investment slurry ratios to capture fine detail and withstand burnout without cracking. This calculator determines powder and water quantities based on flask volume and the manufacturer's recommended mix ratio.