Optic cut/porting finish

[Bulldog]

If I send off a Glock slide and barrel for an optic cut and barrel/slide porting what can I put on the bare metal for rust and corrosion prevention. Looks are not a concern to me and instead of adding to the wait time and cost for them to cerakote or nitride, can I use cold blue or tool black or is there a better option?
Thanks

[Lon]

Cold blue works if you want to save time and money. It’s gonna get all discolored anyway due to the blast from the ports.

[Bulldog]

Cold blue works if you want to save time and money. It’s gonna get all discolored anyway due to the blast from the ports.

Thank you!