Go to your local hardware store and pick up a package of #0000 Steel Wool. Make sure that you pick the finest grade (#0000)  as anything coarser will scratch your glass. When you believe you're finished with a suncatcher or a panel, you can check your work by taking a small piece of the steel wool and rubbing it over the soldered seams. It immediately alerts you to an area that still needs work by 'catching' on it and it will also help clean the solder and make it take patina better.

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