I have been melting and casting silver for many years but just recently the upper surface of my silver ingots go black in the mould and when placed in pickle they turn copper everywhere that was black. I have used brand new safety pickle and only use plastic tweezers in the pickle so I am pretty sure its not contamination. I have also noticed that the borax used during the melting is turning a green/yellow colour instead of the usual deep red/brown.

The only difference in my process is that I have recently started using a Smiths Little Torch with a propane/oxygen mix rather than my traditional butane torch so I was wondering if the problem may stem from the higher temperature that the torch is operating at?

I have tried seven or eight melts over the last two weeks and the problem happens every time and is beginning to really bug me. Can anyone help? Has anyone else had a similar problem?