[TheForge] ( bronze "silverware"

[Peter Fels & Phoebe Palmer]

Good exposition..thank you Bruce!  I'll forward this to them too.
They are statistical biology profs and will appreciate the excess of 
information coming their way.

Bruce Freeman wrote:
> Peter,
> 
> I think you've got the right idea.
> 
> The problem is not metallic copper.  That's pretty inert.
> 
> The problem is the copper oxides - the tarnish.  Copper tarnishes
> pretty quickly in air, especially when damp.  Most of this tarnish is
> the oxide, but other salts can form as well.  Copper salts are readily
> soluble in mild acid (like vinegar, especially in the presence of
> chloride, e.g., table salt).  If this gets into your food, you're
> taking a chance you needn't take.
> 
> Someone else posted that a toxic dose of copper would be about 10 mg.
> I do not know that to be true.  However, it may be well to communicate
> just how much volume 10 mg corresponds to.  Think of an average water
> drop from an eye dropper or such.  That's about 1/20 mL = 0.05 mL =
> 0.05 g = 50 mg.  I would guess that a copper salt will weigh 2 to 3
> times water, so that that same volume of a copper salt (solid) would
> be 100 to 150 mg.  So a volume corresponding to 1/10 of a drop of
> water would be the toxic level, if all these assumptions are true.
> That IS a lot to get off a teaspoon, so this is probably not a
> tremendous worry.
> 
> However, why live dangerously?  Put a couple ounces of vinegar into a
> cup, add a sprinkle of table salt, and stir with the copper teaspoon.
> Voila, the copper will dissolve in the acid.  Rinse with fresh water
> and use the teaspoon for anything you like (except, don't leave it in
> the food for any prolonged period because it could tarnish while in
> use.)  Repeat this procedure before every use and you're safe.  You
> can even reuse the salted vinegar, which eventually will turn blue
> from the copper salts.
> 
> I could have approached this from the other direction and allowed you
> to estimate the copper coming off the spoon into the salted acid, but
> that would require me to look up extinction coefficients, etc., and
> it's too late at night to do that!
> 
> 
> On Wed, Dec 30, 2009 at 2:45 PM, Peter Fels & Phoebe Palmer
> <artgawk at thegrid.net> wrote:
>>
>> Knowledgeable opinions please;
>>
>>
>> Some friends sent me an stylishly elongate, red copper alloy, teaspoon
>> from their dining room set...with the question;
>>
>> Are they safe to use?
>>
>> They were made in Thailand, where such " silver" is common, they said.
>> My first reaction , was to say "no", especially don't leave it to soak
>> in acidic food.
>> They have a new baby and copper oxides can be pretty nasty.
>> Sure would appreciate any more informed advice on this.  pf
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> 
>