OT cleaning oxidation off of magnesium printing plates

I have a few printing plates, up to around two feet wide, and up to maybe 6 inches across. Curved to have been mounted on a maybe 12" diameter roll. Most of them have gotten damp, with some white oxidation 'bloom' in some areas.

Some of the features are very deep cut, so that would be easy to clean up. But some of them are rather shallow 'etched', and I am concerned that any cleaning could destroy the etching.

I will never be printing bags for Purina Dog Chow in great numbers, so I don't worry about them for printing, but I would like to cut them up and make something decorative.

Any suggestions as to what to try to clean up the oxidation? White vinegar was going to be my first choice, on a limited area, to see what happens.

I am aware that the magnesium will burn during cutting/polishing/etc.

Thanks in advance.

The white bloom is probably magnesium hydroxide. I don't know of any feasible way to get the Mg(OH)2 back to metallic Mg. Heating the stuff should change the Mg(OH)2 back to MgO. But MgO is hygroscopic, and attracts water that converts it back to Mg(OH)2. No way to restore it, but you do have to remove it.

I think to get a good method of removing the bloom and protecting the surface will require your google fu and judgement. Obviously this includes a scrupulously dry environment.

The same thing happens to vintage Mg sliderules. Bad karma.

One rather involved method is here:
https://www.arboristsite.com/community/threads/magnesium-alloys.71834/

I don't recommend it.

You could try CLR on a small area and see what it does. I think it is relatively safe to use and might remove some of the oxide.

I use WD-40

Soda blasting used on Mg aircraft components doesnt damage glass ,so it should be OK

Vintage race car guys get into this quite a bit. I've never needed to know so I'm not the guy to ask, except that I've heard that Gibbs aerosol is good for protecting Mag after it's been polished up. The HAMB forum has several threads on restoring magnesium wheels, as an example.

Magnesium castings on motorbikes were passivated with chromic acid,hexavalent of course ,badder the better.

Any acid on magnesium will likely leave you wondering where it went. It is one of the most active metals so, NO ACIDS. Ya hafta wonder how someone could call himself a machinist and know so little about the mediums he works in.

john.k said:

Magnesium castings on motorbikes were passivated with chromic acid,hexavalent of course ,badder the better.

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Passivated? Pretty sure they were anodized with Chromic acid.