If you are looking to "blacken" the solder to match the older naturally patina'd frame, then all you have to do is apply liver of sulphur. You can by a solution from an arts and crafts store, but why pay that much more for what is the same thing just a different bottle. I have a stained glass shop and do repair work. I use liver of sulphur from the hardware store to get the same results as what I got when using Novacan's Black patina for lead and solder. I do use the Novacan Copper Brite patina, but I have never seen older windows with that kind of patina, and honestly unless the solder is really fresh and well cleaned, that one doesn't work too well. The liver of sulphur will also work to black patina zinc frames if any of the framing has been replaced. Good luck on your windows, and thanks for restoring and not replacing!