I am new to jewelry. I would like to try casting silver (pure) in so called green sand. In my research I see that it is recommended to use some sort of flux while melting silver. The most popular and widely available without a doubt is borax (sodium tetraborate if I am not mistaken), however it seems to be for some reason (toxicity maybe) illegal where I live and I cannot get it that easily.
Are there any common materials that can be used as flux for silver melting instead of borax?
I have seen sodium carbonate (wash soda/calcined soda) being sold as some sort of flux and I have read something about sodium hydroxide (lye) being used as flux in some applications. Would these materials be suitable/better than nothing for silver melting or should I not worry about it at all and pure(ish) silver should not oxidize anyway? Or is there anything else that might work?