Airgun Guru: how to use cold blue liquids and gels to repair rust spots

Time Well Spent June 15, 2022

A reader wants to know whether cold blue liquids or gels are good enough to deal with rust, or is re-bluing needed

Q: After shooting in light rain, I foolishly locked my most prized airgun in the cabinet without giving the steel a wipe with an oiled rag. When I took it out, I found tiny areas of rust on the barrel. I’m devastated because the rifle looks like new, apart from the rust spots! I know there’s plenty of ‘cold’ blue liquids and gels available, but would any match the original blue or do I have to send the barrel away for total re-bluing?

The Airgun Guru says:

Some of the modern cold blue products are extremely good, but it can be a struggle to get repairs to blend in with existing blue. If you want perfection, a professional re-blue is the only option, albeit an expensive one.

Having said that, I have seen some cold blue repairs so good that, unless you were told they were there, or the light caught them at a precise angle, you’d be hard pressed to find them. In your favour is the fact that the rust will be on the surface, and should not have penetrated the steel in such a short period of time.

The key to success is preparation. First, gently remove the surface rust using very fine wire wool, which will create small patches of bright steel surrounding the spot that rusted. Make sure the surface of the rusted area is smooth and any minute roughness caused by the rust is gone. Next, thoroughly degrease the areas to be blued.

Before progressing further, get yourself safety goggles and gloves to protect your eyes and skin against splashes, and it’s best to work over a disposable surface, such as a sheet of newspaper.

I prefer to apply cold blue paste rather than liquids as it does not run, and I use a fine artist’s paintbrush. Leave for the time as recommended on the label, then wipe and wash off. Give the area a wipe with an oiled rag, and see how close the colour match is when viewed in daylight.

If the repaired area is too light, degrease it and apply a second treatment of cold blue, and repeat until the desired shade is reached.

All in all, I would suggest having a go with cold blue gel. It isn’t wildly expensive, and may well do the job to your satisfaction. If the results fall short of expectations, then you can consider having the whole barrel, or rifle, professionally blued.

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