The A–Z of Jewelry Casting: Key Technical Terms Every Manufacturer Should Know

In the world of jewelry manufacturing, precision and quality go hand-in-hand. Whether you’re a designer, casting technician, or 3D print expert, understanding the core technical terms used in the jewelry casting process is essential for producing flawless pieces. Below is a curated glossary of essential casting vocabulary every professional should master.

1. Burnout and Mold Preparation

Burnout Cycle

The heating process where wax or resin patterns are burned out of the investment mold inside a kiln, creating a clean cavity for molten metal.

Pyrolysis

The thermal breakdown of organic pattern materials like resin or wax in the absence of oxygen.

Casting Flask

A metal cylinder used to hold the investment material and the pattern during investing and burnout.

Investment Material

A heat-resistant compound, usually gypsum-bonded for jewelry, that surrounds the pattern and forms the mold cavity.

Water-to-Powder Ratio

The mix ratio of water to investment powder, directly impacting mold surface quality and strength.

Isothermal Holding

Maintaining the kiln at a steady temperature during burnout to ensure even and complete wax or resin removal.

Thermal Expansion

The increase in volume of pattern or investment when heated. Critical to manage for preventing cracking.

Refractory Material

The heat-resistant backbone of the investment that can withstand high casting temperatures.

Binder

A component, like gypsum, that binds the refractory material in the investment powder.

2. Flow Dynamics and Fluid Behavior

Fluid Mechanics

The study of how molten metal flows through the gating system and mold.

Reynolds Number

A dimensionless figure that predicts whether metal flow will be laminar or turbulent.

Laminar Flow

Smooth, controlled flow that minimizes turbulence and defects.

Turbulent Flow

Irregular or swirling metal flow that may trap gas or create inclusions.

Back Pressure

Resistance in the mold cavity that can disturb molten metal flow.

Venting

Creating air escape paths in the mold to allow for smoother metal flow and fewer defects.

Mold Fill Time

The duration required for molten metal to completely fill the mold cavity. Critical for detail preservation.

3. Mold Design and Gating Systems

Gating System

The network of sprues, runners, and gates that guides metal into the mold cavity.

Sprue

The main vertical channel for pouring metal, also used to remove pattern material during burnout.

Unpressurized Gating System

A system designed to minimize turbulence by using gradually narrowing flow paths.

Choke Area

The narrowest section of a gating system used to control metal velocity and reduce air entrapment.

Feeder

An additional reservoir of molten metal that compensates for shrinkage during solidification.

Fillet

A rounded transition between surfaces on a model to improve flow and reduce stress concentration.

Casting Tree

An assembly of multiple wax or resin models joined on a central sprue, cast in one shot.

4. Solidification Science

Solidification

The transformation of molten metal into solid as it cools.

Latent Heat of Fusion

The energy absorbed or released when metal changes from liquid to solid.

Heat Transfer

Movement of thermal energy during casting, affecting cooling and solidification.

Heat Sink

A component or mold section that absorbs heat and influences the cooling rate.

Dendrite

Tree-like crystal structures that form during metal solidification.

Nucleation

The first stage of solidification, when solid particles begin to form in the liquid.

Solute Redistribution

Uneven alloy element distribution during solidification, causing microstructural variation.

Monotectic Composition

A unique point in a binary alloy system where one liquid transforms into another liquid and a solid.

Shrink Spot Porosity

A spongy defect caused by insufficient feeding of molten metal as it cools.

Hot Spot

An area in the mold that cools slower than others, increasing the risk of shrinkage and cracking.

5. Microstructure and Casting Defects

Ash Banding

Surface stains or residues caused by incomplete burnout or poor combustion of the pattern.

Inclusions

Foreign materials trapped inside a casting, usually from investment, gas, or contamination.

Porosity

Small voids in the casting. Can be caused by gas, shrinkage, or trapped air.

Gas Porosity

Porosity caused by gas entrapment in the molten metal.

Microporosity

Very small, fine voids that weaken casting integrity.

Shrinkage Porosity

Void formation due to volume contraction during metal solidification.

Cold Shut

A line or crack where two fronts of molten metal fail to fuse completely.

Cracking

Fractures in the mold or casting, often due to thermal stress, poor burnout, or fast heating.

Shell Cracking

Fracturing of the investment mold shell due to improper burnout or expansion of uncured resin residues.

Blowhole

A large gas cavity inside the casting caused by poor venting or degassing.

Oxidation

A surface reaction between metal and oxygen during melting or pouring, causing discoloration or brittleness.

6. Tools and Post-Processing

Crucible

A high-temperature container used for melting metal before pouring.

Rapid Prototype Patterns

3D printed patterns, typically made from castable resin, used in investment casting.

Degassing

Removing air bubbles or gas from the molten metal or resin to reduce defects.

Pickling

A chemical cleaning process used to remove oxides and scale after casting.

Quenching

Rapid cooling of a hot flask in water to remove investment and harden the metal.

Devesting

The removal of the investment mold after casting, usually done by soaking or water blasting.

Annealing

Heat treating a casting to relieve internal stress and soften the metal for further processing.

Leeching

The migration of soluble compounds during burnout or casting, which may affect mold strength or surface finish.

Flux

A chemical used during melting to clean the metal and prevent oxidation.

Sintering

The bonding of particles at high temperatures without complete melting, which can affect mold strength during burnout.

Air Entrapment

Trapped air bubbles that lead to porosity or surface blemishes.

Pattern Wax

Special wax used to create clean-burning casting patterns.

Conclusion: Why These Terms Matter

Jewelry casting is as much about chemistry and engineering as it is about artistry. Knowing the language of casting equips you to troubleshoot defects, improve process efficiency, and elevate the quality of your final product. Whether you're refining your burnout cycle, optimizing your gating design, or experimenting with new resins, these terms provide the foundation for deeper understanding and innovation.