Experiment in progress - Bluing an old gunmetal pocket watch case

[rjenkinsgb]

I was given a 1920s? Limit pocket watch in very poor condition a few days ago. The case back was very badly rusted with deep pitting.

Someone on here advised me that the case was originally blued gunmetal, so I thought I'd see what was possible with it, to make it not quite so bad at least!

Heat bluing seemed out, as the hinge looks to be brazed in place & I did not want to risk it falling apart!

 

I got a bottle of "Jenolite gun blue" to try. First, I sanded the back to remove all visible rust, working from 1000 down to 7000 grade. There was no visible brown at that but still remains of deep pitting, that I though would take too much metal off to fully remove.

An ultrasonic clean in weak Ajax floor cleaner solution for a degrease, as I usually do with case parts, rinses in the ultrasonic then a wash with deionised water followed by IPA to ty and ensure no parts would be "un-wet" in the chemicals.

The gun blue mixes 1:3 with deionised water, then soak the parts for 15 minutes; I used a glass jar just big enough to completely submerse the case, and moved it around every couple of minutes to try and ensure an even effect. I did the bezel with a cotton bud, flat in a jar lid, glass in, and the solution applied around the outside with a cotton bud every few minutes, so it did not get on the inner silvered surface.

 

Everything had a good rinse under the tap once done, then a brief deionised water rinse & dried. The finish it totally matt black as it comes out the solution, with the black sediment rubbing off on anything it touches!

There were some traces or brown rust after it dried, so I tried boiling it for half an hour, as apparently that should convert brown rust to black??

 

Once everything had cooled and been dried out, I tried burnishing the surface with thick kitchen towel dry. That seems to work quite well, removing the loose particles and gradually brining it to a dull shine - but it's quite sensitive to pressure and a crease or fingernail pressure leaves a different level of shine to a smooth pad, until that wears through and creases....

It's not finished, my fingers are aching so giving it a break. I'm hoping the finish will even out with further burnishing, though the residual pits in the back are probably there for good & I'm not sure what to do about the traces of brown that have re-appeared.

The instructions for the chemical blue say it should be oiled as soon as dry, then left to cure for 24 hours - but I'm not sure about soaking a watch case in oil?

I did leave it overnight before boiling & burnishing.

 

It still need more work and detailing! But the effect looks promising.

 

Before:

 

After, still needing further burnishing. All the streaks are pressure marks, where the burnishing has smoother or removed more of the surface material.

I'm hoping that a fine brush will clean the details and edges, where a cloth cannot do anything.

 

 

 

 

 

 

Edited May 29, 2024 by rjenkinsgb