Cleaning stubborn spots of corrosion

I have some letterpress blocks that I need help with cleaning. I have read some of the posts on this site for cleaning and they helped for general cleaning but not for for certain spots of corrosion. These blocks are from around 1900 to 1920 from a farming manufacturer that I collect and they were in the basement of the factory owners house for at least 70 years.

So, is there a way to get the corrosion spots off? Looking at them close up you can see the corrosion is above the image. And another block I have is made of zinc, so what can I do for that one?

They are apart of my local history and are valuable among us antique farm equipment collectors, so I don’t want to risk damaging them. If it’s better to leave them alone i’m fine with that but if anyone knows a way to get the corrosion off, I’d really appreciate the help.

I also have a few hand carved box wood blocks from 1880 to 1890 from the same company that I have some questions about. But, I’ll post about them another time.

image: You can see the corrosion is above the image.

You can see the corrosion is above the image.

image: 20190609_120149.jpg

image: 20190609_120216.jpg

image: This zinc block has some heavy corrosion. Any tips for cleaning this one?

This zinc block has some heavy corrosion. Any tips for cleaning this one?

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J J B (Generally) here in the U.K. we would refer to Your problem as verdigris, the equivalent in copper, of corrosion in iron, steel etc.

It is the result of exposure to the Air in a damp atmosphere, and has partially eaten into the surface of the block/plate.

Tread carefully trying to remove by mechanical means, You will probably remove part of the (damaged) image.
One course of action could be, immerse the blocks/plates in *Cillit Bang* = Amazon etc. virtually worldwide.!

Leave to soak the relevant time, allow to dry naturally, - as You imply, preservation rather than use, the state of the mounting base is a secondary issue, if at all.
For further protection and admiration, coat/spray the surface(s) with Clear Lacquer.

Same process for the Zinc blocks, i.e. gentle as possible decontamination, followed by *Cillit Bang* but finally coated with a smear of Vaseline (petroleum jelly) but pushed into the relief and depth of drive of the blocks.!

Good Luck.