FMF - Friends of Minerals Forum, discussion and message board

[Linda Smith]

I am not sure whether this has been addressed, so I will ask. I collected a copper specimen that is crystalline but unfortunately coated and embedded with a white clay like substance and I also believe calcite. I have soaked this specimen in vinegar as it is a mild acid. I have managed to chip and work some of the matrix from the specimen but when it is dry, it is coated in white. Please help me with how to clean this residue off the specimen.

Thank you for your help

[lluis]

Hi,

Well, I would try the long time honoured "cooking" with 5% caustic soda....
It would take away many silicates and many times even desincrustate many odd thinks

Prepare a 5% solution of caustic soda (normal in commerce is 50% in liquid or say 100% in flakes). You should wear gloves and glasses. The name "caustic" is not freely given :-(

Place the piece inside the solution and keep at 70-80ºC during 3-4 hours, adding more water if needed.
Rising of temperature should be gradual (not important with copper, is not sensible to temperature, but yes for other items), and cooling also slow.
Water could be need to be added to maintain concentration.

When cooled, rinse with plenty water and neutralize.

I did with scheelites from Tête des Éconduits, and it worked very well.....

Hope it serves

Lluís

[Linda Smith]

Hi Lluis,
Thank you for your suggestion. Would you or anyone else know by which name the caustic soda would go here in the United States?

Thank you,
Linda

[lluis]

Hi, Linda

Well, I think in english is caustic soda.
You could ask for sodium hydroxide (chemical name)
Is what is used to make soap from oils (lye) and what is used to clean ovens....

Hope it serves

With best wishes

Lluís

P.D.: really you need to wear gloves and glasses. Caustic soda is a bad beast. If any spill, wash with water and then rub with vinegar...You will smell like a salad, but you will avoid a caustic burn...... :-)

[Peter Megaw]

You can probably get lye or caustic soda at Ace or similar hardware store. If you;re going to heat it use an old crock-pot...

This may well affect the lustre on your copper...although the acid you used may have already done this. In either case rinse carefully and repeatedly in several changes of water when you're done.

I will reiterate the theme of trying mechanical cleaning before resorting to chemicals in most cases...and using the chemicals wisely when you resort to them. It's long out of print, but Sinkankis's "Gemstone and Mineral Data Book" (Wiley) has a comprehensive section on cleaning minerals that lets you readily determine the best technique for whatever you're cleaning. It also has a good section on handling chemicals for those with limited experience,. And an entertaining section on fakes!

I have had considerable success over the years removing white clays from native copper and azurites by a methodical soaking in water with a few drops of liquid detergent (wetting agent) then brushing or power washing away what will come off easily...and repeating until the piece is clean. It can take days, but if you leave it by the kitchen sink and have a go every so often you'll get there...and with much less risk to the specimen.

It pays to invest in a power gun washer...these have come into widespread use since Sinkankis went out of print so he never had a chance to use/recommend one. The price has come down to <$75 on the Chinese models and they are much more powerful than most of the $300 competition. Be careful...you can shoot the fluid through your skin (a painful tatooing effect) ...a rubber glove for the holding hand is a good idea! I have successfully used one of these to take iron-oxides off quartz...no more boiling in HCl or oxalyic acid!

[GneissWare]

I am partial to patinas on Copper, so would try mechanical means before resorting to acids or bases. As Peter suggested, soaking for prolonged periods of time may help loosen the material and will not affect the copper. For example, the Copper from the Ray Mine responds pretty well to this. A water gun is indispensable for cleaning and they are cheap. If you are going to be cleaning lots of minerals, investing in an ultrasonic cleaner is also wise, and can help remove material from minerals that a water gun or mechanical picking would destroy.

If you don't want to buy a water gun right now, an alternative is to use the coin car wash from a considerable distance so you don't launch smaller specimens into orbit.

[bugrock]

Hello,

Regarding caustic I have worked with potassium hydroxide solutions in another realm,
preparing insect specimens for dissection. The caustics generally used are sodium or potassium hydoxide, usually the latter, 10-15% solution. Like most chemical reactions progress is faster at higher temperatures but room temperature is safer. If you must heat such solutions do so in a "double boiler" type arrangement (container or pot of water placed in a pot of water). Do not directly heat these solutions for fear of splatter or "boil over". At best that could damage kitchen items etc. At worst you could loose eyesight or burn your skin!

Another suggestion for cleaning copper is to soak in water a few days, freeze the piece, and then throw it into boiling water. Metals expand faster than "rock" [marix] and you might free some unwanted material from the piece. Some collectors I know are are very patient and just set the piece outside for up to a year and expose it to many freeze-thaw cycles. This of course assumes you live in a climate with very cold winters. Works in Michigan but not coastal California, Spain etc.

Hope this helps,

George

[Linda Smith]

Thank you all for your kind suggestions. I have learned a great deal and think that I will try the least dangerous method and see what happens. Again thank you all.

Linda

[Matt_Zukowski]

Peter - where is the best place to obtain one of these power washers?

[alfredo]

Several dealers sell the high-pressure "water guns". I got mine from John Attard (attminerals) in San Diego, California.

[Peter Megaw]

I get mine from Rock Currier at Jewel Tunnel Imports...they run about $75. But you need wholesale credentials. I like the freezing idea a lot...I'll try that first next time.

[GneissWare]

I can see how freezing would work for the more robust crystals from Michigan, but it seems it might damage more delicate dentritic crystals such as those from Chino, etc. Like every cleaning technique, you need to use the correct one for the individual specimen.

[bugrock]

Hello,

I would like to further the thread of cleaning minerals only because I have been considering the purchase of two items recently, an ultrasonic cleaner and a fabric gun.

Looking for specific recommendations from those with experience using these tools.



In this message I will zero in on the ultrasound cleaners.

I've learned a bit about the ultrasonic (US) cleaners from manufacturers but that only poses more questions. Looking for a cleaner that will both clean up crystal specimens and specimens that have been polished in order to remove the polishing medium at the edges and in the cracks.

If there is a specific site or discussion group that has already considered these details please point me in that direction. The US devices are not inexpensive and I hate to purchase an instrument that will disappoint.

Some specific questions about the US cleaners:

1) What is the best cleaning power in watts?

2) Should I use only water as a medium or add cleaning solutions as recommended by manufacturers? These additives I gather are detergents and wetting agents that help cut grease and grime from machine tools, instruments, metal parts etc. But are they appropriate for use on minerals or should I just add a bit of detergent or other mild wetting agent to the water bath?

3) Many of these units are sold with heaters. Is that feature really necessary?
Would assume it speeds the process.

4) The units also come with timers. When undertaking a cleaning job what time interval should you try on the first pass?

5) It is recommended to protect the cleaner's transducers by suspending the object (s) to be cleaned above the bottom of the tank. Any thoughts on what works best, wire basket, perforated tray, beakers and beaker holder? Also, should you keep mineral specimens separated from each other?

6) Are there minerals that can be damaged by US cleaners?


Thanks all for your guidance.

[GneissWare]

1) I use a Sonicor model SC-200H with heater. It is a 4 transducer, 3.3 Amp unit with tank dimensions of 9.375 x 11.75 x 5.5 inches.

2) I only use water. Distilled water is used for rinsing. I sometimes use a drop or two of Ivory soap, as it is free of most chemicals, and seems to help the cavitation effect.

3) I never use the heater, as the water heats up on its own with use. I usually fill the tank with room temperature water and once it starts getting warm or really dirty, I change it out. Some minerals will break if exposed to too warm of a water bath, so I try to avoid temperature shocks.

4) Mine does not have a timer. Most specimens are in the cleaner for no more than a few minutes. I watch everything and once the water doesn't seem to be getting any dirtier, I remove the specimen.

5) It may be wrong, but if the specimen is delicate I hold it by hand in the ultrasonic--feels wierd but you get used to it. More robust specimens I set right on the bottom of the tank. The majority of the tank wear is due to the ultrasonic action degrading the tank. I always rinse the tank out when I'm not actively using it and dry it out.

6) Are there minerals that can be damaged by US cleaners? Lots! Jamesonite for certain, Millerite probably, some Wulfenites probably. You need to test each piece.

[John S. White]

A friend of mine is a very good specimen cleaner. One trick that I learned from him is to soak the specimen overnight, at least, in soapy water before using either a fabric gun or an ultrasonic cleaner. This may soften whatever you are trying to remove and help with the cleaning.