h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I'm looking at a couple of recipes for cleaning silver or copper and want to understand how they work. I'll post the recipes in the next post and then ask my questions.

recipe #1 silver

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Silver Cleaning Tips

Q: Do you have any silver cleaning tips? Thanks. Trish, CO

A: Here is a simple, magnetic method for cleaning silver. Fill a pan big enough to hold the silver with water (a corn steamer, for example, for big pieces). Add the silver, baking soda, salt, and aluminum foil. Let the mixture sit for an hour or so. If you stand over it, you will notice a slightly rotten egg smell. The tarnish will magnetically be pulled from the silver onto the aluminum foil. Rinse the silver in hot water and polish dry with a soft cloth.

If you have remaining spots and tough-to-clean areas, dab some white supermarket-type toothpaste into your hand. Your natural body oils are part of this formula, so make sure your hands are dry and haven't been washed too recently. Massage the white toothpaste onto the spots. Rub it in until the discoloration is gone. The toothpaste will turn gray and start smelling like metal. A small amount of toothpaste goes a long way when mixed with oils; if you don't want to use your bare hands, add a drop or two of olive oil to the toothpaste. Just plain baking soda will also work for cleaning silver. And to keep silver from tarnishing, store silver that is not being used out of the light, either wrapped in soft felt or cloth.
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http://www.heall.com/body/healthupdates/environment/nontoxiccleaning.html


My questions:

(a) which of the initial ingredients are necessary? I've seen similar recipes with just baking soda and aluminium and water. Some say boil the water, others say just use hot water - does it matter? Is it solely a magnetic thing or is there a chemical thing going on too?

(b) what is the toothpaste doing? What ingredient in the toothpaste is the essential one? How would body oil be useful?

(c) will this be removing any silver? (eg if done repeatedly over time).

(c) will it work for cleaning other metals? Which ones?

recipe #2 copper:

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Lemon juice

A great cleaner thanks to the citric acid it contains. When used with salt, it is especially good for cleaning copper and brass, although use it with care, as it can lighten the shade of the metal if left on for a long time or not rinsed off well.
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http://www.guardian.co.uk/chemicalworld/story/0,,1220125,00.html


My questions:

(a) why would the colour lighten?

(b) would this work with silver or other metals? why/why not?




kea.

The aluminium foil thing is likely electrochemical - the two metals in contact with the salt solution form a electrical cell, and having the two metals touch each other completes a circuit and gives rise to a cleaning action which is chemical in nature, but driven by electricity.

Ok, so sodium chloride or sodium bicarbonate, doesn't matter which as they're both salts reacting with the aluminium and silver and creating a charge?

Would that work with all metals then? Presumably there is something about aluminium, or aluminium and silver?

hmmm, maybe I also need to understand what is being cleaned off. The tarnish, is that an oxide? So the electrochemical thing affects the... what?

http://www.darylscience.com/Demos/Silver.html

Goes into some detail about what might happen with the aluminium route.

However,
http://www.silversmithing.com/care.htm
http://www.preservation.gc.ca/howto/articles/silver_e.asp
http://www.manl.nf.ca/Silver.pdf
all suggest it might not be a great method of cleaning.

Doesn't polishing with a bit of toothpasta bring silver to a good shine?