Metal Coatings

[Steve Wardley]

I have several items of woodworking tools and machinery parts that have a thin black coating on them, a coating that I can only describe as being like engineers blue or a patina only its black.
Now due to a lack of forethought on my part some of this coating has suffered some light rusting due to bad storage in my loft, I've managed on the whole to wire wool this rust off but it's also thinned out some of this coating and I would like to re-treat these parts with something to prolong their life but I'm not sure what this stuff is.
Does anyone have an idea what this patina might be or could suggest an alternative, perhaps just a tool wax or similar ? Paint won't be any good as some of these parts have to slide up and down posts etc.
Cheers guy's

 

[ED65]

On older stuff in particular a black coating is likely to be a black oxide finish, but there are other chemical treatments that can produce a durable ultra-thin black finish on steel.

It's not absolutely vital to refinish any worn black parts to keep rust at bay if you can wax them, but if you do want to restore a black finish probably the simplest option is using Kurust from Hammerite. The surface of the parts should be cleaned with cellulose thinners or a good brush cleaner beforehand to remove any lacquer or oiling.

 

[Lons]

You can do it with manganese phosphate or gun black / blue but you'll still want to wax or seal the finish afterwards.

I treated some steel hinges years ago and the finish was very durable.

 

[chiokli]

I've used this gun blue solution on bare steel before to form that black patina:
Phillips Professional Cold Blue - 250ml £11.99 from Amazon

Wax or a spray lacquer over the top for full coverage from rust.

There is also the linseed oil on hot metal approach:
Jordan Smith - How to finish steel with linseed oil - YouTube

But probably not for your woodworking tools and spare parts. Does leave a nice finish though!
(I'm working my way up to adding links to posts)