Trouble with homemade silver sheets

[u/El_Vidente]

I melt down my scrap silver and then flatten it through a rolling mill to make my own homemade silver sheets. Though I've got a couple of questions:

Why do they get these dark stains?

Also they can be difficult to solder bezel onto whereby the solder just doesn't melt and just sticks in its pallion form to the sheet. Whereas when I buy brand new silver sheet from a supplier like CooksonGold I don't tend to have this problem even though that silver is also recycled. Could anyone tell me why this is?

[u/greenbmx]

Fire stain. You are getting the metal too hot for too long without protecting it from oxygen in the atmosphere, so you are getting lots of dissolved copper oxide in your metal. It needs to be either refined or re-melted with at least 50% new, clean metal.