Problem for Black colored Titanium Bolts

These are the black anodized titanium bolts,really don’t know how it happened.After negotiating with our anodizing factory,usually this problem will happen for black coloring by anodizing.Before shipping,all looks good,but don’t know what happened,there is purple color generated.So in the future,for all black colors,we will color them by PVD coating.And we suggest all of you,if you order titanium products with black color,you should buy them in PVD coated black color.