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    The Mysterious Case of the Exploding Shellac Can





    Two reasons you should always check the date of manufacture when purchasing shellac.

    Shellac CansRemember how your mom taught you never to eat anything out of a bulging tin can? You know, the botulism warning? Turns out it goes the same for shellac as well -- sort of.

    One afternoon I found myself in the workshop during my lunch break. My aim was to use some clear shellac purchased that morning at the local hardware store to finish some walnut and maple picture frame molding I had put together the previous night. I set the can down on my finishing table, broke out a flathead screwdriver and proceeded to pry off the lid when, WHAM, the top shot off like a champagne cork and a shower of shellac droplets filled the air. After a short trip to the bathroom to throw out one of my now-contaminated contact lenses and use the emergency eyewash, I figured I might as well give the moldings a quick coat before setting off to purchase new lenses. Trouble was, my clear shellac was actually . . . brown!

    No worries, I thought, I'm sure it's just this particular brand. It'll dry clear. In short order I realized that I now had some beautiful walnut moldings with maple stringing that had been stained into oblivion. A day later, I used a small block plane to shave off the top layer of wood, beneath the shellac. Phew - problem solved.

    Oh, and the shellac can? Well, it was manufactured in June of 2005, making it well past its prime.

    Straight to the Horse's Mouth
    Shortly after returning from a trip to the eye doctor, I hammered out an email to the manufacturer of the shellac in question, hoping to get an answer as to what might have caused the buildup of gas that resulted in that explosive can. As it turns out, most of these cans are lined. The slightest flaw in that lining ("even a micro flaw") can allow the shellac/alcohol mixture to react with the now-exposed metal of the can, creating gas and thus, pressure. Zinsser, for one, is aware of the phenomenon and is working out a solution regarding the linings in their cans.

    That said, it's important to understand that the bottom line is, this can was old....very old, and while the "maximum shelf live of Bulls Eye Shellac is 3 years, Zinsser agrees with my recommendation of not keeping shellac longer than one year past the date of manufacture..

    So flip those cans over and check your dates whenever making a purchase! 

    Has anyone out there had a similar experience with old shellac? If so, I'd be curious to hear about it in the comments section below. 


    Ed_Pirnik