Gunked-Up Brass

Five years ago, when I inherited my Dad's shop after he passed away, I brought home a few things that were pretty unique. One of them was this...



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My Dad once told me that this set of concrete stamps belonged to his grandfather, who was a civil engineer with the Michigan Department of Transportation. He was one of the designers of the Davidson Freeway, which is the oldest freeway in the United States. As far as I can tell, these stamps are in the original box, and still are pretty gunked-up with concrete dust and dirt.

I didn't think much of these, until I was showing them to my father-in-law yesterday. He made the comment that I should try and clean them up a bit and see what they look like. I wasn't expecting much when I pulled out my Dremel with wire wheel, but got a bit of a surprised when I saw some shiny, brassy-looking color below the grime. So at that point, I fired up the bench grinder and spent a couple of minutes at the wire wheel. BOY, was I shocked with what I found!!!



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I did some searching based on the markings on the stamp, and found the website for Schmidt Marking Systems. They claim that, "...Geo. T. Schmidt, Inc. has been a worldwide leader in permanent metal marking machines, technology and services for over a century." Sounds like I got the right place! I'm going to contact their public relations department to see if I can find out more information about this set of stamps.

My question to you guys has to do with how to get all of the dirt off of the stamps. The wire wheel and Dremel do a pretty good job, but I can't get the grime out of the crevises. Is there something that I can soak these things in? I want to make sure that I don't damage the stamps, but I'd love to get them all sparkling again.

Thanks for your help!

- Keith

You could try some swimming pool cleaner stuff called muriatic acid. It’ll dissolve the concrete residue. Nasty stuff so wear eye & hand protection. I don’t know if it’ll effect the brass or not, so test it in a non-conspicuous spot.

Maybe a better option would be to have it bead blasted (not sand blasted). That will clean it up nicely but you’ll have to rebuff.

Maybe the best option would to leave it like you have it. It looks pretty good from here.

Keith....Bruce's recommendation about muratic acid might work. I'd try it on another piece of brass first....say a brass washer etc......if nothing bad happens....then try in on these.

Any slightly acidic solution should work, some are more aggressive than others. HCl (muriatic) is pretty aggressive, I'd probably cut it half and half with water (add acid to water, NOT water to acid) to get it down to 14% or so - last time I bought some it was a 28% solution. It would be a good idea to drop the parts in a neutralizing solution (baking soda and water) after soaking too, so that you don't start to get further oxidation in the pits where its hard to rinse all the acid out. A very thorough rinse with tap water would be needed at a minimum.

PS- those look more like bronze to me, which would be a better choice for making concrete stamps than brass

John Downey said:

PS- those look more like bronze to me, which would be a better choice for making concrete stamps than brass

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I think you're right.

Hmmm ... will the electrolysis process work with bronze?

The muratic acid might work. Be sure to use it in well ventilated area in addition to the other cautions mentioned. Before I tried that I would try letting them soak in Coke for a couple of hours and rinsing with water. That is a good use for diet pop that is past the best by date. Coke can do good work on things like corroded battery terminals and slow drains.

Muratic acid can be nasty stuff if you are not careful with it.

i would bypass the acid and glass bead blast them at a low pot pressure. i did a lot of this when i did defense work.

I think I would call some one who restores antiques before I did anything else.

Bead blasting, and muriatic acid would both work. as would blasting it with ground walnut shells, a medium that gets used on cleaning woods and other delicate surfaces.