Which Copper is Best for Enamelling

TU2 oxygen-free copper (ASTM C10200/10100) is the preferred choice for firing enamel because it minimizes oxygen and impurities like phosphorus, preventing bubbles, cracks, and adhesion failures during high-temperature enamelling.​

Why Avoid Standard T1/T2 (ASTM C11000) Copper

Standard T1/T2 electrolytic copper—equivalent to ASTM B152 C11000 (Electrolytic Tough Pitch, ETP) at 99.90% minimum purity—contains trace oxygen (up to 0.04%), phosphorus (typically ≤0.002-0.01%), and inclusions like sulphur or micro-voids. These defects lie dormant until enamelling's 700-900°C firing: oxygen forms flaky copper oxides that release gases, while phosphorus disrupts oxide layers, causing persistent bubbles or cracks that return even after grinding and refiring.​

TU2's Superiority (ASTM C10200 vs. C11000)

TU2 matches ASTM B152 C10200 (Oxygen-Free Electronic, OFE copper): ≥99.99% purity, oxygen ≤10 ppm (0.001%), total impurities ≤0.01%—vastly cleaner than C11000's 99.90% spec. This eliminates hydrogen embrittlement and gas evolution, yielding a continuous black oxide layer for flawless enamel adhesion. Fine grain structure reduces thermal stresses, perfect for Canadian enamellers needing zero defects.​

Phosphorus Defects from C11000 Copper

Phosphorus in C11000 (T1/T2)—added as a deoxidiser—creates enamelling havoc:

• Forms low-melt eutectics that boil gases, producing bubbles or "boil" pits.​

• Spalls oxide films, trapping gases underneath: pinholes, fishscales, blisters result.​

• Industry data shows C11000 yields 2-5x more defects than C10200/TU2, as phosphorus segregates to grain boundaries, amplifying stress cracks.

Check our C10200 >99.95 Purity Copper Sheets for enamelling.