Combustion temperature — aluminothermic reduction
25°C
Mold-Integrated Exothermic Iron Casting

Iron from
thermite.

Aluminothermic reduction of iron oxide within ceramic shell investment molds produces cast iron directly from thermite combustion. The mold system is built around 3D-printed PLA positives that contain the combustion chamber, vents, sprues, and sculpture in one form.

Reaction Fe₂O₃ + 2Al → Al₂O₃ + 2Fe
Mold system Ceramic shell investment
Positive material FDM-printed PLA
Iron yield (empirical) ~33% of charge mass
Fabrication sequence

From print to cast iron

The ceramic shell investment mold is consumed in the casting event and is configured for a single use.

PLA positive assembly showing combustion chamber, sprue, sculpture geometry, and vent risers
01 — POSITIVE
PLA print
The complete mold assembly — combustion chamber, sprue, sculpture cavity, and vents — is printed as a single PLA positive. The print establishes all internal void geometry prior to shell application.
Ceramic shell investment applied over PLA positive assembly
02 — SHELL
Ceramic shell investment
The PLA positive is dip-coated in ceramic slurry and stuccoed in sequential layers until sufficient shell thickness is achieved. The slurry remains workable in a stationary bucket between coats — no motorized agitation required.
Looking down into the open combustion chamber after PLA burnout, ceramic shell wall visible
03 — BURNOUT
PLA burnout
The shelled assembly is fired to remove the PLA positive, leaving the ceramic shell as the mold. The shell is preheated prior to thermite loading to reduce thermal shock at ignition.
Thermite charge materials — two 5lb jars of United Nuclear cast iron thermite, ignition mix, and sparklers
04 — CHARGE
Thermite loading
Commercially available thermite is loaded in granular form into the combustion chamber. Charge mass is calculated from the chamber volume and the measured density of the granular material. Ignition is initiated using a sparkler inserted into a bed of thermite ignition mix at the top of the charge.
Thermite ignition — aluminothermic reaction at approximately 2500 degrees Celsius
05 — CAST
Ignition and fill
Ignition initiates the aluminothermic reaction at approximately 2,500°C. Molten iron drains by gravity through the sprue into the sculpture cavity and exits at the vents. Al₂O₃ slag separates and floats above the iron.
Cast iron batwing form after mold break, held in hand
06 — FINISH
Mold break and finishing
The ceramic shell is broken away from the solidified casting. Sprues and vents are cut from the sculpture form. The mold is not reusable.
Mass balance

Charge and yield

In practice, approximately a third of the thermite charge mass is recovered as iron — below the theoretical maximum, with the difference attributed primarily to material ejected during ignition and iron trapped within the solidified slag layer.

The combustion chamber is sized using a volume calculator that sums the sculpture cavity, sprue, and vent volumes to estimate the total iron needed to fill the mold. A small additional volume at the base of the combustion chamber is factored in as margin, ensuring sufficient iron yield to fill the casting completely. Sprues and vents are removed from the finished piece after casting.

The weight of the charge is calculated from the chamber volume and the measured density of the granular material.

Parameter
Basis
Value
Theoretical Fe yield
Stoichiometric
~52%
Empirical Fe yield
Measured
~33%
Bulk thermite density
Empirical
1.394 g/cm³
Combustion temp
Literature
~2,500°C
Al₂O₃ slag phase
Co-product
~52% of charge
Combustion chamber sizing tool

Volume calculator

Import an STL of your sculpture to calculate its volume, then use the cylinder solver to determine the required combustion chamber height for a given diameter. Yield factor and density parameters are editable.

Shell system and charge

Materials

Ceramic shell slurry

The ceramic shell slurry uses a colloidal silica binder (Remasol SP-30) with a zircon flour prime coat and fused silica backup coats. The addition of xanthan gum as a suspension agent eliminates the motorized drum agitator typically required to prevent slurry settling — the slurry remains workable in a stationary bucket between dip coats.

Incorporating xanthan gum into colloidal silica requires controlled dispersion: small quantities are sifted through a 200-mesh sieve onto the surface of the Remasol and whisked in incrementally, a process that takes approximately one hour per 35 grams per half-gallon of binder. The resulting mixture is then pressed through the sieve a second time using a rubber spatula to break up agglomerated lumps, after which it is allowed to rest overnight so the xanthan gum fully hydrates before the remaining binder volume is incorporated and the refractory fillers are added. Between dip coats, Remasol SP-30 is applied to the shell surface by spray bottle as a wetting agent prior to stucco application.

Thermite charge

Commercially available thermite — a granular mixture of iron oxide and aluminum powder — is loaded directly into the combustion chamber. The weight of the charge is calculated from the chamber volume and the measured density of the granular material.

Component Function Application
Remasol SP-30Colloidal silica binderPrime + backup
Zircon flour (–325 mesh)Prime coat refractory fillerPrime coat
Fused silica flourBackup coat fillerBackup coats
Fused silica stuccoInterlayer adhesionAll coats
Remasol SP-30 (spray)Wetting agent between coatsBetween dip coats
Xanthan gumSuspension agentSlurry additive
Sculpture

Cast forms

The casting process is form-agnostic — the sculpture geometry is determined by the PLA positive, which can be modeled to any geometry that can be printed and invested. Current work targets abstract geometric forms derived from triply periodic minimal surfaces, including the Schwarz CLP and Fischer-Koch S surfaces. These geometries are generated computationally and output as STL files for print preparation.

Mid-South Sculpture Alliance ConFab — October 2–3, 2026

Documentation

Images from the ConFab demonstration will be added here after October 2026.

— image —Shell construction
— image —Thermite charge
— image —Ignition
— image —Cast result
Direct contact

Get in touch

Questions about the process, materials, or upcoming demonstrations can be sent directly using this form. Messages go to Andy Huss and are not publicly visible.