[TheForge] ( bronze "silverware"

[James Binnion]

FWIW LD 50 for copper chloride is 584 mg/kg. This means 50% of the  
rats die when given a dose of copper chloride equal to 558 mg per  
kilogram of body weight. The 10-12 mg toxic number I quoted is the  
upper limit for daily intake in an average adult, that doesn't mean  
you are going to die or start peeing green at 15 mg but it is more  
than your body can deal with under normal conditions. For comparison  
the LD50 of ferric chloride is 315 mg/kg so better git rid of all that  
iron cookware and heaven forbid you have any stainless steel as the  
nickel in it when dissolved by chlorine in the salt acid solution has  
a LD50 105 mg/kg. Yes it is easier to dissolve the copper but  
nonetheless stainless is attacked by salt and will corrode.

Given a choice I would use silver utensils but I don't think using  
copper ones is that big a deal. As Mike said just don't eat the green  
stuff :-)




On Dec 30, 2009, at 8:59 PM, 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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>
>
>
> -- 
> Bruce
> NJ
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James Binnion
jbin at well.com