@ murtle - can you just heat the frame to get the spots?
I reckon it's 'Oil-Bluing'.. dip it in some oil / chemicals first.
Just heating. I did it at school. Use a torch and heat the metal. I did it at school. Colours go from red to blue to white. White means you've melted it. I wouldn't be surprised if that bike snapped at some point because of the heated spots.
Just heating. I did it at school. Use a torch and heat the metal. I did it at school. Colours go from red to blue to white. White means you've melted it. I wouldn't be surprised if that bike snapped at some point because of the heated spots.