Wax burnout is one of those processes that looks simple on paper and humbles you in practice. Get the ramp rate wrong, fire too fast, or use the wrong kiln, and you end up with cracked investment, incomplete burnout, or a flask full of carbonized wax residue that contaminates your pour. Here's how to set up a clean, consistent wax burnout process from the start.
In lost-wax casting, you pack your wax model in investment (a plaster-silica mix), let it set, then fire it in a kiln to burn out the wax and leave a cavity for molten metal. The process has two phases: wax elimination and flask preparation.
During wax elimination (roughly 300°F–700°F), the wax melts and drains out, then vaporizes and burns. This phase requires the kiln door to be slightly vented so combustion gases can escape. A kiln with a vent hole or cracked door is essential here — trapping those gases causes incomplete burnout and leaves carbon deposits in the mold cavity, which shows up as inclusions or surface defects in the final casting.
During flask preparation (typically 900°F–1350°F depending on the metal being cast), the investment is brought up to casting temperature and held until the mold walls are uniformly hot. A cold spot in the mold causes the metal to freeze prematurely before it fills the cavity.
Rushing the ramp is the most common mistake in wax burnout. Investment is essentially a ceramic shell — heat it too fast and steam pressure from moisture cracks it. A typical safe ramp from room temperature to 300°F is 100°F–150°F per hour. From 300°F to 700°F (active wax burnout), 200°F per hour is usually safe. From 700°F to casting temperature, you can push faster — 300°F–500°F per hour.
The exact ramp schedule depends on your investment manufacturer's specs, flask size, and metal type. Larger flasks and thicker investment walls need slower ramps. Always check your investment data sheet.
Any kiln can technically do wax burnout, but a kiln designed for the process makes it cleaner and more repeatable. Key features: a vent hole or door provision for combustion gases, interior dimensions suited to your flask sizes, a controller with multi-stage ramp-and-soak, and elements positioned to heat the flask evenly from all sides.
Our Hot Shot 7GW Wax Burnout Kiln ($1,795) is built specifically for lost-wax and investment casting workflows. It handles small-to-medium flask sizes, runs on 120V, and includes the programmable controller you need to automate your burnout schedule. The HS-7GW variant offers the same core capability in a slightly different configuration.
Before buying a kiln for burnout work, measure your largest flask — diameter and height. Your kiln interior needs to accommodate that flask with at least 1" of clearance on all sides for even heat circulation. Loading flasks too tight against kiln walls creates uneven heating and cold spots on the mold surface.
If you cast both small jewelry pieces and larger sculptural work, consider a kiln with interior dimensions flexible enough to stack flasks vertically when doing smaller runs.
Wax burnout produces smoke and fumes, especially in the 300°F–600°F range when the wax is actively combusting. Even with a vented kiln, you need good studio ventilation — a window fan or exhaust vent pulling air away from your breathing zone. Don't skip this step.
Ready to set up a clean burnout workflow? Browse our wax burnout kilns and get in touch if you want help matching a kiln to your flask sizes and metals.
{"one"=>"Select 2 or 3 items to compare", "other"=>"{{ count }} of 3 items selected"}