[TheForge] ( bronze "silverware"

[Peter Fels & Phoebe Palmer]

Applause for this expositions finale!
Thank you Bruce and Jim!!!!
A deep bow to you.

James Binnion wrote:
> 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
> 
> 
> 
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