Increasing 800 silver to 925
Calculations and methods to increase the silver grade by adding fine metal.
At a glanceAntique 800‰ silver tableware (800 parts per thousand, or 80% pure silver) is very common in European estates. To transform it into 925‰ sterling jewelry, the melter must add fine metal.
Formula: Fine metal to add = Weight × (Target purity − Current purity) ÷ (1000 − Target purity)
Example: For 100g of 800 silver → 925: (100 × (925 − 800)) ÷ (1000 − 925) = 100 × 125 ÷ 75 = 166.67g of 999‰ silver to add. The final total mass will be 266.67g at 925‰.
Practical Steps: Weigh and document the incoming lot. Check the assay if necessary by touchstone testing or chemical analysis. Melt together with the fine metal in a clean crucible in the presence of borax. Verify the final assay before delivery.
Use the alloy calculator below to automatically calculate masses according to your configuration.
🧮 Alloy & purity calculator
Alloy and purity raise calculator
Calculate exactly how much fine metal or master alloy to add to reach your target purity.
Add pure Gold/Silver (Fine)
+ 166.67 g
New total weight
266.67 g