To harden sterling silver, heat it to 600°F (316°C) for 30–50 minutes in a kiln or furnace. Air-cool the sterling silver before pickling. The hardness will be equal to the hardness achieved by cold-working it to a 50% reduction (or ¾-hard). If you want to make your sterling silver harder than ¾-hard, you must physically reduce the cross-sectional area using the chart below.
| Rockwell Hardness | Common Term | Reduction in Cross-Sectional Area | ||
|---|---|---|---|---|
| Fine Silver | Sterling Silver | Wire | Sheet | |
| 43 | 70 | Soft (annealed) | 0% | 0% |
| 65 | 80 | ¼-hard | 21% | 11% |
| 72 | 82 | ½-hard | 37% | 21% |
| 74 | 83 | ¾-hard | 50% | 29% |
| 76 | 85 | Hard | 60% | 37% |
| 80 | 87 | Spring | 84% | 60% |
Example: If you start with a dead-soft wire and reduce the cross-sectional area by drawing it down 50%, your material will become ¾-hard.