Repairing brass street lamp + soda blasting

[cardiffrob]

Well, it wouldn't fit easily into any other forum...

My father has this old lamp from when he lived near Poole and managed to salvage one of the fancy street lamps that were being phased out. Massive cast iron body and a beautiful brass top to it. The years have taken their toll and now it has fallen to me to see if it can be rejuvenated.

There is a lot of copper sheet used in the design and it has many thick layers of paint, lots of rock-hard putty and encrusted bird poo to come off. So, first question is "should I try soda blasting copper and, if so, should I buy a huge 25kg bag of it"? Hard to know how much it needs. I have the compressor and gun plus a small Clarke blasting box but the grit and glass I have used before lasts for ever. Same with soda?

Next problem is the one of polishing the copper once the paint is off. Shouldn't be too hard to get a shine on most of it but I'm guessing that it has been soft soldered. Leave the solder showing or buff it away? Does the solder suffer from the salt air environment?

Once polished, what would be the best way to preserve the shine for a long time? Any brand name suggestions would be most welcomed.

Oh, and quite amazingly every single bolt and screw has come undone!

Thanks

Rob

 

[Maker]

Can't really give you any advice myself but it sounds like an interesting project, got any pictures?

 

[MattF]

Personally, I'd be a bit leary of cleaning that up too much. I'd be going with getting the paint off but leaving some age to it. The best method I've found for doing brass/copper is by popping them in the electrolysis vat which I use for derusting. Give them upto a few hours in there and it's usually possible to give them a scrub up with a brass bristle brush to get a cleaned finish which retains some patina. It should also remove the paint, unless it's one of those awkward ones which clings like s**t and seems almost impervious to anything.

I definitely wouldn't try hiding any solder either. If there are blobs anywhere, (unlikely), then flat those out, but otherwise just leave it visible as applied.

If you're wanting to protect it from oxidising, either Linseed oil or lacquer it when done. Personally, I'm not a fan of lacquer as if it gets scratched, it's a ball ache to work around when you start getting spotty oxidisation. An oil you can merrily remove or recoat if needed.

 

[cardiffrob]

The paint is seriously hard. Cellulose thinners didn't shift it, hence the thought that soda might work.

 

[MattF]

Try a bit of caustic soda on it and see if that softens it. If a decently strong solution of that, (I'm guessing you know all the safety precautions to take with that stuff), doesn't soften it, then blasting is likely your only real option bar burning the stuff off. If the caustic works, electrolysis should shift it too, in a safer than flesh destroying manner than the caustic. If the paint is really tough, even soda blasting may not shift it. I seem to recall a rtbcomp for one saying that certain finishes need some prep work even when more aggressive blasting materials are used, in some of the blasting related threads. I think he uses that that Methyl? something or other stuff. Brake fluid tends to be another thing that's decent at shifting most paints. Does need to be left on for a decent while to soften the paint up though, and might need several applications with scraping soft stuff off inbetween.

 

[rtbcomp]

Methylene Chloride. It was the staple ingredient of the traditional Nitromors. It can be bought on Ebay.

Don't burn it, you'll distort the copper and possible spoil the soldered joints.

Blasting with fine glass grit and following up with glass beads might work, again be careful because blasting will heat the surface, although copper may dissipate the heat OK.

I'd steer away from electrolysis, it acts on the metal not the paint and you may end up with a few litres of a copper salt and no lamp.

 

[MattF]

Methylene Chloride. It was the staple ingredient of the traditional Nitromors. It can be bought on Ebay.

Cheers. I couldn't remember what it was called for the life of me.

I'd steer away from electrolysis, it acts on the metal not the paint and you may end up with a few litres of a copper salt and no lamp.

It won't bother copper. I've done various pieces using electrolysis, and have intentionally left a few scrap pieces in for days to check for any detrimental effect on the metal. There's absolutely none that I've been able to discern. I trust it enough to pop antique brass plaques in there nowadays, so as you can guess, it ain't detrimental.

Saying that though, I do try to limit the amount of time I leave stuff in there for, just as a precaution, until I find some specific factual info on that point. Plus, it generally only needs a hour or two in the vat to start notably removing oxidisation from brass and copper. It's nowhere near as entrenched as rust.

 

[DanielW]

Throw up a pic and lets see if you're going to devalue its potential value?

 

[DanielW]

This the one?
http://www.englishlampposts.co.uk/media/wysiwyg/Lamp_Posts/Refurbished_reclaimed_lamp_post.jpg

 

[rtbcomp]

It won't bother copper. ...........

Depends on the electrolyte - try using copper sulphate and see what happens

 

[Maker]

Methylene Chloride. It was the staple ingredient of the traditional Nitromors

Dichloromethane is the name usually used, different name, same stuff.

 

[rtbcomp]

I can't spell "Dichloromethane"

 

[Maker]

I can't spell "Dichloromethane"

Well you managed it there.

 

[graffian]

Well you managed it there.

And I can't spell methylene chloride, so I put synstyp

 

[cardiffrob]

Victory!
I found a tin of Nitromors in a cupboard that was clearly quite ancient. It was left overnight on the copper top of the lamp with tissue paper keeping it in place. By morning it was hard but when I washed it down it seems to have stripped off the topmost layer of paint quite well.
A nylon brush has helped but there are still corners that I can not get cleaned out. They'll also be a bu66er to polish up. Would glass beads at low pressure be a decent finish, as in a polished look or a rough look? I have a large tub of them somewhere.

I'll try for some pics later.