Green crud on a brass model


srrcoalburner

srrcoalburner

Member
A buddy brought a couple of brass models over for me to paint. One is an Empire Midland Southern Railway 2-8-2 # 4501. The other is a Westside Great Northern 4-6-2 with Belpaire firebox and an all-weather cab. The E.M. will be a snap. The Westside however, looks like it has some extensive foam damage on both the loco and tender. It is bright green and almost looks like moss has grown on the surface of the brass. It is quite thick...I took a hobby knife and scraped down to the brass underneath. Its probably 1/8 th of an inch in places.
I am tempted to stick the thing in the blasting cabnet and go at it with aluminum oxide but I wanted to ask and see if anyone had a better solution. Is there a way to remove the 'crud' chemically?
Thanks,
David
 
the green is likely the remnant of the foam used to pack old brass. The foam is notorious for deteriorating over time, sticking to everything and just being a general pain. Some isopropyl might be a good wipe down that won't hurt anything. Mineral spirits is a bit stronger but fairly safe. Too strong of a solvent and you may create a bigger mess, so stay away from lacquer thinner for example.
 
Sounds like corrosion, but I'm not sure what's the best solution.
I'd think Brasso or Noxon would work.
 
If it is bright green, almost turquoise, it is verdigris, or the oxide of copper. It should not be present on a fine brass model. It indicates one of two likely possibilities: acid solder flux was used and not neutralized effectively, or the brass was exposed to air with cool temps and high humidity causing condensation. The condensation in turn made contact with an acid of some kind that caused the oxidation of the copper.

http://en.wikipedia.org/wiki/Verdigris
 
David;

If it is as thick as you say it is, more than likely its the dregs of the foam it was originally stored in.

Being Westside, I doubt if its any solder or flux residue. The loco is a Japanese import and definitely wouldn't have had any shoddy workmanship.

Best thing is to tear it down, you may have to scrape areas like around the brake shoes, to get to screws and such, but its worth it.

After its stripped down, then throw it into a new batch of lacquer thinner, and after the stuff is dissolved, pour out that batch of thinner and soak it some more in another new batch. Repeat until any "stickiness" caused by the foam residue is gone.

Then run it through the blaster, but make sure you get both inside and outside. This will ensure the dissolved foam is completely off the model.

Call me if you need any help!
 
Thanks to all. C.J., Robert and I will probably run this model up there for you to look at. Its in pretty rough shape and is covered completely on one side of the engine and tender. We just have to find a day when we can all get together...the main problem being with my hectic work schedule. robert got a SWEET deal on these models and the 4501 is cherry. I checked it for frame warpage and if there is any it is minimal. It runs better than either of mine. The gearbox was dry and I added some Labell oil and now it sounds like a pea-sheller like both of mine. What gives? You take care, Brother!
David
 
The aluminum oxide in your blasting cabinet might be a bit harsh. I use baking soda for blasting brass engines. Cleans them up really nice. Get the baking soda from your local bulk food store - much cheaper than the boxed stuff.


Mark.
 
220 grit or finer aluminum oxide won't hurt the brass, and gives a nice tooth for painting. I use it all the time. Glass beads also work well in a booth, but you have to be careful of heat buildup. I've also used pumice available in a gallon can from Paasche. Never tried baking soda. Stay atound 60 psi. Higher pressures will get you into trouble with glass beads or aluminum oxide.

Anything 1/8" thick is going to be foam residue, and I would agree with CJ. Lacquer thinner first. That should get rid of the gunk and any sticky. Lord only knows how much money I've spent at Reboxx on replacement foam sets and new boxes! No manufacturer from the period is immune from this that I have found. I had a factory painted Tenshodo Crown SP Cab Forward damaged by deteriorating foam. I was lucky and caught it early. I also had a model shipped to me and the foam deteriorated to dust during shipment leaving the engine and tender to bang against each other during handling. I had extensive repairs to make. When I opened the box I nearly had a stroke!
 
Thanks, Mark and Espee...I have been under CJ's tutelage for a couple of years now. Like most padawan learners, I have strayed from his teachings only to find that he was correct all along. I have been using the aluminum oxide 220 grit @ 30 to 50 p.s.i. depending on how stubborn the mess is. CJ has taught me a lot and I am greatful to have his instruction. He got me back into brass after I had given up the first go-round. I dont know weather to thank him or kick him!:D
 
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