This thread sparked a question in my head. Imagine that you are in a situation where you need to dispose of you wallet seed backup, but it is etched on a steel plate - how would you do it? The easiest answer is likely acid, but not everyone has access to it, and depending on the steel plate, it might be even highly resistant to corrosion. Another option is to damage it mechanically - in many of these steel plate products you are supposed to etch the words, so it should be possible to erase them or render unrecognizable. But it's likely hard to do thoroughly and traces of the words could remain.

Any more ideas?