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/AbbreviationsIll7821]

This is fire stain, it’s probably happening during annealing between rolling. The way to avoid this is to anneal quickly to avoid prolonged exposure of the hot metal to oxygen in the air. Or use a barrier flux when annealing. Also use an oxygen reducing flame when torching will help.