Yellow-firing ceramics are almost always caused by Fe2O3 in the raw materials — and the feldspar or nepheline flux is the most common source.
Understanding This Defect
Here is the step-by-step diagnostic process our technical team recommends to customers: Step 1 — Fire individual discs of each raw material in your formulation (clay, feldspar/nepheline, quartz, talc, etc.) at your standard temperature. Compare whiteness. The most yellow disc identifies your primary iron source. Step 2 — Request our K200 sample (Fe2O3 0.08%) and fire a disc under identical conditions. If our disc fires significantly whiter than your current feldspar, the iron in your feldspar is confirmed as the cause.
Solution & Prevention
Step 3 — Make a test body replacing your current feldspar with our K200 (use 82% of the weight — see conversion guide). Fire and compare with your standard body. The improvement should be clearly visible. Step 4 — If the improvement is satisfactory, transition your production to K200 (for premium white) or K100 (for standard production). Both our grades achieve dramatically lower Fe2O3 than typical dry-processed feldspar..
