How to identify lead crystal glassware?
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!