Bicycle bottom bracket spindle material choice.

[PeterT]

I bought some from Kens, JAX brand. But it was for ferrous. I don't see it listed here though. It was ~45$ but going back a few years.
http://kengem.com/cat302_1.htm

product details from company. I could see no difference to KBC or the ?blue bottle? you see at gun supply places
https://jaxchemical.com/shop/jax-iron-steel-nickel-blackener/

 

[DPittman]

This c old blue stuff is available at Canadian Tire in small quantities

 

[Swharfin']

Was meaning a small bottle of Birchwood Casey @ $14 or so - been awhile since I've bought.
I use it by the Q Tip for touch ups ,shouldn't take more than a tsp for painly's project.