I have several hundreds small pieces of brass that do have quite a bit of value but many of them are covered in a collection of oxides.
They are about the size of a 9mm shell with a bit of ceramic / steatite and a little brass screen inside (protected).
I have a rock tumbler that I would like to use to clean them so they can be sold.
Trouble is, I'm not sure of what polishing media would be best.
a) It has to be soluble
b) It has to be of aproximately the same hardness as the brass and steatite (not much!)
c) It shouldnt corrode the brass or make the existing corrosion worst.
There are several chemicals I thought of, salt being the most obvious but I'm afraid it'll tarnish the brass.
Magnesium Sulphate can be found in pharmacies in crystal form.
What do you think about MgSo4 hydrate ? Can you think of something else ?Deathunter88 - 22-10-2019 at 07:22
What about no media and just letting them grind against each other?Herr Haber - 22-10-2019 at 10:44
Not a bad idea !
I gave it a go for 30mn and the water came out green.
I'll let it run longer and see in a few hours.
I'd rather do it with a mild and abrasive because the parts are threaded and I'm not sure grinding against each other will get in there (thread is
outside).
There is also some writing but I doubt I'll get that.
I could get over a thousand Euros from that so any suggestion for abrasive or liquid / solvent to make a suspension or "mud" for lack of a better
word would be good.
I wouldnt even mind putting them through a Soxhlet to remove everything used in the process. Show me some Madness wg48temp9 - 22-10-2019 at 14:42
Some people have used granular cat litter, pieces of rubber/wood chips with polishing compound. Check out youtube.
Of cause none of those are soluble in water.elementcollector1 - 22-10-2019 at 18:35
My vote is for Epsom salt. Other options might be baking/washing soda (if they weren't so soft), and maybe sugar (again, unclear on the hardness,
which is the most important quality for abrasive polishing IIRC).bobm4360 - 22-10-2019 at 20:35
Try citric acid soak, 10g/100ml. With one piece, time until it looks good, then rinse with water. Dry with very low oven or hair dryer. Works great
on cartridges and similar sized brass pieces. When you have a good idea of the time it takes, then do bulk.
[Edited on 23-10-2019 by bobm4360]Herr Haber - 23-10-2019 at 08:16
Thank you all for all your inputs and suggestions.
Thanks for that link wg48temp9. I got a ball mill a couple months ago and now I go to sleep thinking about what I am going to put in next.
Pieces of rubber... I can think of a few use for that !
I got about 100 grams of big MgSO4.H20 crystals that I will try on another batch to see if it helps clean the thread.
I am not sure I can locate my citric acid but I have some sulphamic acid that might do the trick. I never had really good results from these methods
though. But sulphamic bath followed by drying + short time in the ball mill with Epsom salts might be a good combination.
So far, by just rubbing together in water I have cleaned most of the oxydes and debris that stuck to the brass but the threads remain green.
There is one positive aspect of this green oxyde: it makes the letters stand out.
I could stop the project "as is" but got to try some of your ideas Herr Haber - 24-10-2019 at 05:20
Well, sulphamic acid wasnt that great.
The brass turned "pink". Same thing happened years ago when cleaning .50 bullets so I should have known.Alkoholvergiftung - 24-10-2019 at 11:48
I only know very deluted nitric Acid to "Burn" brass yellow. Than it gets it s Shining like new brass cartriges.wg48temp9 - 24-10-2019 at 15:04
Well, sulphamic acid wasnt that great.
The brass turned "pink". Same thing happened years ago when cleaning .50 bullets so I should have known.
Most acids tend to preferentially dissolve the zinc and leave amorphis copper, that's the pink color. Herr Haber - 25-10-2019 at 03:11
I used Epsom salts yesterday and... it worked beyond expectation on the parts that I tumbled with water the day before.
Of course it becomes a powder very fast and clogs every hole (important since the parts are antique gas burners) but it also dissolves well enough.
The threads were mostly clean and the burners being new but 70+ years old people will expect some tarnishing.
I'll be getting some more Espsom salt. I still have a few hundred burners to clean
