Your low-grade copper wire is normally alot of plastic compared to the copper which is why it pays so low. Computer towers have small trace amounts of gold in them, sinks are normally a low grade stainless alloy. And when it comes to brass there is so many different types it would be impossible to narrow it down. First step would be is it an Alpha-Brass or an Alpha-Beta-Brass. But odds are the local scrapyard buys it as yellow brass. Hope this helps.