oxidizing in heat treat

[Freds Edge]

I have heat treated my 2nd CPN 154 blade and have some oxidation on the blade , a slight rainbow affect . Is this a common thing or am I not getting a good seal on the foil or not enough paper to burn off the oxygen ? Any help is appreciated .

 

[Ausbrooks]

If you're getting just a rainbow color and not a dark oxidation layer then in my experience you have a good foil seal.