Back to Ganoksin | FAQ | Contact

Formula to raise silver fineness

Does anyone have the formula to figure the amount of pure silver
needed to raise the fineness of coin silver or lower to sterling
silver. I have some .625 fine Olympic coins that I want to raise to
.925. I know that 1 oz of .625 silver should have approximately 12.5
dwt ( 19.4375 grams ) of fine silver and 7.5 dwt ( 11.6625 grams ) of
alloy so to raise 1 oz of.625 to .925 I should need 4 ozs of pure
which would give me 92.5 dwt of silver and 7.5 dwt of alloy but there
must be an easy mathematical formula to use.

Greg DeMark

Here’s the general formula:
RP = Required Purity (0.925 for Sterling Silver)
CP = Coin Purity (0.625 in your case)
CW = Weight of coin silver
PW = Weight of pure silver

RP = (CPCW + PW)/(CW + PW)
Cross multiplying gives: RP
Re-arranging gives: PW*(1 - RP) = CW*(RP - CP)
Therefore: PW = CW*(RP - CP)/(1 - RP)

Since you have 1oz of 0.625 silver and you want 0.925 silver, the
weight of pure silver required is: 1*(0.925-0.625)/(1-0.925) =
0.3/0.075 = 4

Regards, Gary Wooding


Mass of fine silver = (M(R - H))/(1000 - R)

This equation will give you the mass of fine silver required to
raise the Olympic coin silver to Sterling silver.

M = The weight of metal on hand (in grams)

H = The precious metal content of the metal on hand in parts per

R = The precious metal content of the required metal

Slot in your figures, and you should be good to go

and example of using the equation :-

Let’s say you have 10 grams of coin silver, and you want to know how
much fine silver you need to improve the precious metal content.

(10(925 - 625) / (1000 - 925) = 3000 / 75 = 40 grams of fine silver.

Regards Charles A.

Thank you for sharing this Charles and Gary. Two from
the many great minds and artists on Orchid.

Greg DeMark