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I would like to identify if a wine glass is made of lead crystal (a destructive method is allowed). Lead crystal is said to be eroded by dishwasher detergent. I don't have a dishwasher, what causes the stains? Could I quickly identify lead crystal by exposing it to hot caustic soda?

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    $\begingroup$ A first hint could be a high density and a high refractive index. $\endgroup$
    – user7951
    Jul 20, 2019 at 15:45
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    $\begingroup$ I tried both but did not succeed, that is why I am wondering about a chemical method. $\endgroup$
    – jkien
    Jul 20, 2019 at 15:51
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    $\begingroup$ Normal glass has a density of $\approx 2.4 \; \mathrm{g/m^3}$ and lead glass $\ge 3.1 \; \mathrm{g/m^3}$ so I am surprised that you have found this to be non-discriminating. The difference in refractive index will be harder to measure unless you have the apparatus but you can measure the density with scales and via Archimedes' principle. $\endgroup$
    – porphyrin
    Jul 20, 2019 at 16:28
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    $\begingroup$ I was unable to determine the volume of the wineglasses sufficiently accurately, using kitchen utensils, partly because of air bubbles. Therefore the density test failed. I submerged the wineglasses in (sunflower) oil, hoping that the visibility of lead crystal would be different, or its reflectivity. But in reality I saw no differences. $\endgroup$
    – jkien
    Jul 20, 2019 at 17:18
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    $\begingroup$ Air bubbles? I don't think that can be a problem. Your glass will have a volume in the range of several tens of millilitres. You mark some translucent plastic box which is so small the glass just fits in completely, fill it to the mark with water, place the glass in it, and pour off the water above the mark onto a scale. Voilà, weight in g is volume of glass in ml. Or, perhaps simpler, use a cheap 5 ml plastic syringe to take out the excess water. $\endgroup$
    – Karl
    Jul 20, 2019 at 20:56

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Since a destructive method is allowed, the other suggestions did not work for you (despite being excellent, especially the Archimede's scales suggested by @porphyrin) and you have hot caustic soda (aka $\ce{NaOH}$), I suggest this plausible method (which, thankfully, I have never had to use). First, crush a small amount of the suspect lead glass, trying to get it a finely crushed as you reasonably can. Second, mix that crushed glass with solid $\ce{NaOH}$. You do not need much of the mixture: a teaspoon (or a couple of grams) should suffice. Third, do a fusion of that mixture. A crucible would be used in a laboratory, but you can improvise using a small cast iron skillet. They sell very small ones (4 or 5 inch diameter) at some hardware stores. Absolutely do not use aluminum because the $\ce{NaOH}$ will destroy it!

You need to do the fusion at moderately high temperature, such as can be obtained with a charcoal grill, gas grill or a campfire. You may need to be a bit inventive on this and take care to avoid having anything spatter onto yourself! This is where a grill cover is very helpful. Fourth, let the fusion cool down and add some white vinegar to neutralize the $\ce{NaOH}$. You can add an excess, but don't get carried away: dilution is not your friend. If lead was present, you should now have some 'sugar of lead' (lead acetate) in solution. Fifth, hardware stores usually sell inexpensive test kits for lead (from leaded paints). So use one of those to test your neutralized solution for lead.

What about false positives? Do the whole thing over with crushed glass that definitely does not contain lead. It would be best to do this 'blank' first, to avoid contaminating the new little skillet (which, by the way, can be cleaned, seasoned anew, and used for its orthodox purpose).

I have not tried this and I hand-wash my lead 'crystal' single malt glasses, so best of success!

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