In the world of precious metal analysis, accuracy is everything. Whether you’re recycling automotive catalysts, refining electronic waste, or dealing with raw ore, knowing the exact amount of valuable metals like gold, platinum, palladium, or silver is crucial. Among the oldest and most reliable techniques for this is Fire Assay—a method that has stood the test of time for over 2,000 years.
At Metralis, we combine time-honored methods like Fire Assay with cutting-edge technology to deliver precise, trusted results. In this article, we’ll take you through what Fire Assay is, why it’s still relevant today, and how it works—step by step.
What is Fire Assay?
Fire Assay (also known as Cupellation) is a high-temperature chemical process used to separate and measure precious metals from other materials in a sample. It is regarded as the gold standard for accuracy in determining the content of gold, silver, and platinum group metals (PGMs).
Unlike surface-level techniques like XRF (X-ray fluorescence), Fire Assay analyzes the entire sample, giving a far more comprehensive and accurate result—making it ideal for applications where even small variances in metal content can have significant financial implications.
Step-by-Step: How Fire Assay Works
- Sample Preparation
The process begins with collecting and homogenizing a representative sample—often in powdered form. Accuracy at this stage is critical, as inconsistencies here can affect the entire analysis.
- Mixing with Fluxes
The sample is mixed with a combination of flux materials such as litharge (lead oxide), borax, silica, and soda ash. These help in:
- Isolating impurities
- Binding non-precious elements
- Forming a clean separation between metal and slag
- Fusion in a Furnace
The mixture is then heated to temperatures exceeding 1,000°C in a clay crucible. At this stage:
- The lead componentof the flux reduces and absorbs the precious metals.
- Other elements are driven off or absorbed into the slag(waste layer).
- Formation of Lead Button
As the melt cools, a dense lead “button” forms at the bottom, containing the precious metals. This is physically separated from the lighter slag.
- Cupellation
The lead button is placed in a porous cupel and reheated in a cupellation furnace. The lead oxidizes and is absorbed into the cupel, leaving behind a small bead—the pure precious metal content.
- Weighing and Analysis
The bead is weighed and is further analyzed via ICP-OES for detailed compositional breakdown. The weight and composition are then used to determine the precise metal content in the original sample.
Why Choose Fire Assay?
- High Precision: Ideal for materials with low precious metal content
- Bulk Analysis: Measures total content—not just the surface
- Reliable Standards: Accepted by global laboratories, refiners, and regulators.
At Metralis, we use Fire Assay for unquestionable accuracy — in automotive catalysts, electronics, and high-value scrap metals.
Fire Assay + Modern Tech = Even Better Results
While Fire Assay is ancient, it’s far from outdated. At Metralis, we enhance traditional Fire Assay with modern instruments like ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) to verify and cross-check results. This hybrid approach gives our clients the most accurate and trustworthy analysis possible.
Trust Metralis with Your Precious Metals
When accuracy matters, Fire Assay delivers. And when speed, reliability, and transparency are also required—Metralis is your trusted partner.
Want to know how Fire Assay can improve your metal recovery operations?
Contact our lab team today to discuss your needs or schedule a sample analysis.
