One factor that may come into play is the type of brass used. As brass can actually contain more or less zinc, perhaps some models are more prone to oxidation. I must admit that the model that gave me trouble was an old Katsumi engine, probably made in the sixties. Still looks and runs great (with a new motor...)
DSC_0117 on Flickr
Since then, I have just been using alcohol with a toothbrush to clean up any residues on my brass engines. I then apply a light coat of diluted shellac. The boiler gets to sit in the oven for 20 minutes... As mentioned earlier, locos with oxidation get the sandblast treatment prior to the alcohol wash.
I typically take the engine apart, mostly to change the motor as I don't care much for these old open-frame motors. It's just really hard to achieve low speeds with them... And changing them is a cinch if your are willing to keep the plastic tubing approach. Some say that the tubing provides less torque than an u-joint, but I can't really tell. I don't airbrush the wheels as I got sick of the power-pickup problems that result from that. But recently, I've been adding all-power pickups to my tenders, so maybe I should go back to the airbrush for the drivers... I could also use a decoder with a keep-alive caps, but I prefer to add power pickups - I just get better control and the regular decoders are much cheaper. Drivers finished with an airbursh do look better than just the regular brush...
Simon
Something I have not tried instead of the lemon juice is the likely 'active ingredient' which is now commonly available: powdered citric acid. Again be sure to heat it with salt; I'd be careful how strong, but gentle 'lemon juice' strength might be sensible to try first, and then sprinkle more powder if the job isn't getting done.
Looking back at the original post: this acts as if there is something on the towel - perhaps detergent residue, perhaps fabric softening of some kind. There's really not much way that active acetic acid will remain on the surface after the indicated soapy-water rinse (but of course that's the point of passivation after pickling with any acid).
In my experience, one sure-fire way to get green spots on brass was to use any of the Simple Green products, Do not let those anywhere near something intricate made of brass components.
What I recommend trying is to turn the oven on to about 200 degrees, let it preheat, and turn it off. Then put the model on a support 'inside the shell' and put it in the warm cavity to dry. I used to use wood shavings as a support for clock parts, but you have to be careful of the source of those shavings so I won't 'recommend' it. Try to keep the 'piece' as much as possible out of contact with anything as it dries.
No salt...
snjroyI dipped a model in vinegar once and got that green oxidation problem.
I dipped a model in vinegar once and got that green oxidation problem. I used a hobby sandblaster with soda to remove it. Never again did I use vinegar.
What I always used was lemon juice (or strong vinegar) loaded with salt (NaCl) as a pickle, followed by sodium bicarbonate passivation and thorough rinsing.
I was taught to heat the acid to dissolve a better proportion of salt and give faster working. I would not leave the piece in there very long, but use a fine bristle brush or perhaps a small hank of everyone's favorite quad-ought steel wool on specific stain areas.
Incidentally Korean groceries have special 26% vinegar which is over 4x the 'special strength' 6% sold here. This would be interesting stuff to try on a degreased stripped model. (The bottle notes that this is NOT for human consumption undiluted - an interesting understatement.)
doctorwayne Actually, the bi-carb is probably a very good idea: I wouldn't be surprised if the green deposits were caused by an acid-based flux when the loco was soldered together. Bi-carb works great on cleaning the battery terminals in your car, so it just might do a good job on those green spots, too. Mix it with a little water to form a paste, and let it sit for a while before rinsing it off. Wayne
Actually, the bi-carb is probably a very good idea: I wouldn't be surprised if the green deposits were caused by an acid-based flux when the loco was soldered together. Bi-carb works great on cleaning the battery terminals in your car, so it just might do a good job on those green spots, too. Mix it with a little water to form a paste, and let it sit for a while before rinsing it off.
Wayne
That may be so. I mentioned it because I use it as an "abrasive", as opposed to a "chemical neutralizer". It's very good at mechanically scrubbing off schmutz. And it is fully water soluble, so it will be GONE, later. If properly rinsed.
In this case, you would not let it sit. Only.
Ed
7j43k...As far as the green spots, I think it's safer to remove them. I think I'd try bicarbonate of soda, and a toothbrush. Bicarbonate is only mildly abrasive, and it will rinse off (and also disolve) with, yes, warm flowing water. Lots of it, of course....
The green color has me thinking of a copper reaction (copper being in brass).
If there's a problem with what you did, I would guess with the "soap". I recommend using a very plain dish detergent. And then rinse it until you are bored to tears, and rinse it more. In running WARM water. You want to get ALL the detergent off.
As far as the green spots, I think it's safer to remove them. I think I'd try bicarbonate of soda, and a toothbrush. Bicarbonate is only mildly abrasive, and it will rinse off (and also disolve) with, yes, warm flowing water. Lots of it, of course.
Depending on your tapwater quality, you might want to do a final rinse with distilled water. My water here is fine, and I never do. I suppose it's possible something in your tapwater is causing the problem, as opposed to your "soap".
I have had one problem over the years with surface prep: I sprayed a first coat onto a plastic flat car, and the paint surface got all "puckered up". It WASN'T orange peel. It's as if the paint was trying to get away from itself--little flat places separated by ridges. I assumed it was either using the wrong dish soap or not rinsing well enough.
Using alcohol is an interesting idea. Good idea? Beats me.
I Recently tried Painting my first brass train and things where looking great until I took off masking tape and chunks of paint came with it. I'm 90% this was the fault of the factory clear coat which was not in the greatest condition. So I decided to try again so I strip the model useing hardware store laquire thinner, soaked it in grocery store vinegar for a few hours then washed the pieces in soapy water, rinsed them and left them on a clean towel to dry over night. When I woke up this morning there where tiny green spots mosty where the towel and the train met and some some water would have been sitting before it dryed. I can get the green specks by dipping in vinegar and scrubing with a toothbrush but comes back as it drys. I cleaned it off again and this time blow off most of the water with compressed air I did not have time to get all the water but this did seemed to help. I think I'll try this again but I'll do a more through job with the compressed air and clean in isopropyl alcohol instead of soapy water to reduce drying time. This is my first time painting brass so this is all very new to me has anyone else experienced this? I have not read or seen any pictures on the internet. should I just paint over them if I cant get rid of them?