FP & Andy,
I am not an expert at taking pictures and have no access to sophisticated equipment & lighting. From what you are both saying, the finish is of a blue type of some sort not phosphate. The outer surfaces of the bayonet do not look as blue as the scabbard & or bayonet blade.
A question? How many bayonets have you seen where the numbers, dates & manufacturers stamps have been scrubbed off of the bayonets and scabbards?
Why was such extreme rework done at this period in the war?
Richard Kuchta