I recently bought a new set of bagpipes with nickel ornamentaion. The pieces are cylindrical with soldered or brazed seams. The problem is that there are yellow marks on the pieces that I can’t remove with either solvents or abraisives. The marks are roughly circular (about 5mm in diameter) and there is one yellow line about 2mm wide the length of a seam. Can anyone tell me what this is and how to remove it? Thanks.