It was Gever Tulley and his book
50 Dangerous Things (You Should Let Your Children Do) that first got me thinking about giving children an opportunity to break glass, something that is typically forbidden, yet endlessly fascinating.
Our set-up is a little different than Tulley's, but just as effective and fun. We wrap bottles or jars in a thick towel, then try to smash them one-by-one with a rubber mallet. We start by talking about broken glass. Most of the kids already know that it is sharp and will cut their fingers and they all have already experienced broken glass in their day-to-day lives, so it usually only takes a few minutes to get everyone up to speed. Yesterday's key cautionary tale was from a girl who's mother had recently cut her foot when she walked into the kitchen while her father was sweeping up the remnants of a drinking glass he had dropped.
As we do with all potentially injurious things we work with at the workbench, like hot glue guns, we spend a lot of time both up front and while engaged in the project discussing the potential hazards and how to avoid them.
The children are generally impressed with how difficult it is to break a jar or bottle using our method. They have all been sufficiently warned about the fragility of glass, so they are expecting that it will break easily, but these containers were designed not to break too easily, so for most kids it takes all their might to succeed. Yesterday, we formed a sort of cheering section for each child as they took their whacks, shouting advice like, "Harder!" and "Swing the mallet over your head!"
When a child succeeds, usually after a dozen or more whacks, she knows it. We then carefully open the towel to study the results, looking with our eyes and not our hands. We noted yesterday that the bottoms of the containers typically survive our blows, because the "glass is thicker." We study how small the bits of glass can be. "It's as small as sand," one boy remarked. Sometimes the labels held a section of shattered glass together which we found surprising given that we didn't expect paper to be "stronger" than glass. We put a leaf in a jelly jar and marveled at how it survived with only a "tiny hole" even as the jar was reduced to smithereens.
We discovered that the weakest point of most containers is the open end, a discovery that the children then used to increase their success rate. One boy offered a very detail theory for this in which he surmised that the open end "is full of air and so is easier to break," whereas the bottom didn't have any air so it is harder to break.
Our biggest discovery yesterday, however, was that under certain conditions, glass can be stronger than wood. After a dozen or more whacks of progressively greater impact, the handle of one of our mallets snapped in two, an accident that startled and amazed us all.
Breaking glass is something that most of us spend our lives avoiding, even as it is all around us, especially in urban environments where shards can show up pretty much anywhere outdoors. And like anything else that is plentiful, it's worthy of our closer study, cautiously.
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