My local grocery store started carrying bottles of Irn Bru, the Scottish soft drink whose flavor I can only describe as "metallic, but also tutti-frutti". (They were in the ethnic food aisle next to Greek dolma and German spaetzle.)

Not trusting that the Irn Bru had necessarily made the journey to Colorado in a timely manner, I checked for an expiration date. When I found it, I was excited, and not just because it hadn't expired yet: the expiration date appears to have been lasered on.

A plastic bottle of Irn Bru, tipped on its side to show the expiration date near the bottom. The letters are smooth and frosted-looking, and curve around the side of the bottle.

The laser heats the surface of the bottle just enough to remove some of it, changing the surface texture from smooth to rough and making the letters and numbers stand out.

I've been seeing more and more products with laser-marked lot numbers and expiration dates, including glass bottles, aluminum cans, and paper cartons. Although the laser system is expensive, it's better than ink stamping at making marks on surfaces that are curved, or still hot, or still wet. The telltale sign of a laser-marked product is a line that colorless (etched on glass or clear plastic) or white (etched away the dyed surface of a dark paper carton). If you run a fingernail across the mark, you may be just able to feel the edge of the etched area.

So far I've identified probable laser marking on cans of Diet Coke, cartons of Diet Coke, bottles of Bulleit Rye and Angel's Envy (I swear this is not all I drink but only where I've seen laser - I think the company has to be large to afford the laser.) Let me know if you've spotted laser marks on other products!

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