Use this Excel engine calculator to figure out the needed 90% coin silver and pure 99.9% silver to alloy your own sterling silver for pouring bars and/or making your own sterling silver jewelry. Just input the desired total weight of sterling in grams and the program will tell you how much coin silver and pure silver to add.
This Excel program was designed and made by my dear friend Michael P. By using this engine, you can calculate the needed coin silver and pure silver for a specific total weight of 92.5% sterling silver. 92.5% of silver is the minimum required for sterling silver. Previously, I was using equal parts of coin silver and 99.9% silver to obtain 95% sterling silver or two parts 90.0% coin silver with one part 99.9% fine silver for 93.3% sterling silver. Michael noticed that there was a noticeable waste of silver in this method. By using this program, you are able to obtain exactly 92.5% sterling silver.
In addition to the engine calculator are the mathematical equations and excel programming so that you can check the work yourself if you desire. Also, there is a table showing possible ring size, hole size, and ring band width ratios.
In order to work the program, your computer will need to be able to read Excel. Here are some downloads for this if you do not have excel: