Corrosion on Letterpress plates

I have a huge stack of unmounted halftone plates (more than likely magnesium) that have corroded over time. I did research how to clean plates, but most people seem to be referring to simple image cuts, and not an intricate halftoned image.

I’ve tried denatured alcohol, brasso, mineral spirits, and Nevr-dull (this was awful on the halftone, the fibers just caught in the fine dots), all with plenty of elbow grease and a stiff bristled brush and tooth brush. All the plates shine up well, but the spots of corrosion just stay.

Any tips and tricks would be appreciated, and if it’s a loosing battle I’d like to know that too.


p.s. I understand that to prevent further degradation I should put these plates in a ziplock or cover with saran wrap with WD-40.

image: White clouds of corrosion

White clouds of corrosion

image: More clouding and haloing.

More clouding and haloing.

image: Dark corrosion

Dark corrosion

image: Haven't tried to print it yet, but I'm thinking that marks will show up.

Haven't tried to print it yet, but I'm thinking that marks will show up.

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i have used my very flat block (approx 2” x3”) with 1500 grit to just touch the surface of the plate. I use it with wd40 or any light oil, even water if in the field.
with half tone plates, you cannot push hard or too many passes, but it exposes new metal. my halftone plates are for foil so i don’t know what yours will do.

I have used a light coat of cooking spray and stored them in sealed bags for 30 years. Vaseline works to, very light coat. I have some that are over 70 years old and nothing wrong. The air does this.

To clean off any corrosion, I’d take a soft tooth brush and remove any flakes. AS far as removing an damage, that can’t happen.

I think Theo Bell is right, once damaged you can’t bring them back. There is an eraser that is called an engravers rubbing stone, I have used them on my foil stamping dies to remove light corrosion but a halftone is fine dots and once messed up would be almost impossible to bring back. I was told if you can’t find the engravers rubbing stone you can go to a hobby store and get the erasers that the model train guys use to clean their train tracks, I have used them but they are a little more abrasive than the rubbing stones so you have to go a little easier with them.

With either zinc or magnesium (these plates are probably zinc but might be either), the oxide is much less structurally sound than the base metal.* Once oxidation starts, the metal oxide will begin to flake or crumble off. This is how corrosion spreads. The flaking reveals fresh metal to oxidize, which flakes off, revealing fresh metal to oxidize, etc.

This means the print surface may well be entirely gone where there is corrosion. If the plates were large solid areas you might be able to polish the surface down to fresh metal all the way across, but because of the complexity of the halftones there is likely no solution short of printing the plate as is, scanning the result, recreating the missing pieces digitally, and having a new plate made.

* Interestingly, most cupric alloys like brasses and bronzes have a more durable oxide form than the base metal. This is why it’s usually a Bad Idea┬« to polish the verdigris off statuary, why water pipes are often made of copper, and why there’s such a thing as marine brass.

Michael Hurley
Titivilus Press
Memphis, TN

Thank you everyone! I’m going to try the eraser next, if that doesn’t work then I will progress into some other things I have read about.

Whatever happens I’ll be restoring these plates to type height and printing them imperfections and all! They are still gorgeous images.


i have a method that works great I use a homemade soda blaster it gets down in every knook and cranny and does not harm the metal at all ill post some photos of before and after its quite impressive


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