Not sure what you are asking, Welding copper? Do you want to make a still out of copper and have it safe to drink the moonshine? Well I've never seen anyone weld copper. I have used silver solder on copper. Before the Hunt brothers jacked the price of silver solder it was about 20x cheaper that today's price. When a copper line is attached to the steel on an A/C compressor it is silver soldered. There shouldn't be any lead in silver, unless it's made in China. You will need to get the proper flux and cleaners when using silver and an oxy/acet. torch to get it hot enough.
Post a pic of your still.