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I have a marble cup which I drink wine from. If I leave a little bit of wine in the cup and wait maybe 30 minutes, the wine becomes discolored and appears black (photos attached). My conjecture is that this is the acid from the wine interacting with the calcium carbonate of the marble to produce calcium choloride? If so, is it toxic to continue drinking wine from the cup? Thanks.

liquid cup

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    $\begingroup$ No. You're fine. People have been drinking wine from vessels made from calcium carbonate to glass to various metals since, well, the dawn of wine. Your precipitate or concentrate is not hazardous to your health but might be unpleasant to taste. I recommend diluting it with more wine and continuing on as you were. $\endgroup$ – Todd Minehardt Jul 24 '16 at 3:06
  • $\begingroup$ Romans had their drinking water arrive to them in lead pipes. As a result they lived shorter than they could have. $\endgroup$ – sixtytrees Jul 24 '16 at 3:09
  • $\begingroup$ Todd - thanks for your comments. Do you happen to have a source for the precipitate or concentrate being non-hazardous? I am curious why I couldn't find any mention of this anywhere on the Internet. $\endgroup$ – Adam Kapelner Jul 24 '16 at 16:00
  • $\begingroup$ @AdamKapelner - Not offhand, but it could also be something from the wine, too, which I would expect to be non-hazardous. Not all of them are filtered to the same degree and you might be seeing some leftovers from the wine. If you want to get a little more quantitative, I suggest filling the cup with water and testing both the water and the water that has sat in the cup - there are cheap water testing kits such as this one which might put your mind at ease. $\endgroup$ – Todd Minehardt Jul 25 '16 at 23:11
  • $\begingroup$ @ToddMinehardt - tested it with the product which comes with bacteria, pesticides and lead tests. No lead... Any other toxic compounds I should be worried about? Can you think of any other byproducts of wine + marble I should be concerned about? $\endgroup$ – Adam Kapelner Sep 6 '16 at 16:05
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CaCl2 and magnesium are not toxic at these levels. In fact NIH suggests around 1 g calcium per day: https://medlineplus.gov/magazine/issues/winter11/articles/winter11pg12.html

Marble itself is predominantly calcite or dolomite, that is carbonates of calcium and magnesium. Marble also contains other elements. We can't say if these other chemicals are safe just by a photo because composition of marble varies.

When you bought this cup - did they say it is safe to drink from it? Supplier should know if the material is safe or not. If you didn't get assurance that it is safe then you should assume it is not.

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    $\begingroup$ Hi sixtytrees, I bought the cup in India and I have no information about it. So I should assume it's not safe? $\endgroup$ – Adam Kapelner Jul 24 '16 at 16:01

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