...I'm a bit miffed I wasn't given the opportunity to rectify the problem myself and am worried I'm now going to get landed a hefty "repair bill". My liability insurance will cover this but can anyone offer any insight into cast iron particles "penetrating" glass ?
You are right, they should have given you the chance to correct the error. As they have failed to do that, you are not obliged to pay.
The whole thing is iffy anyway; very few things will "penetrate" glass, Fluor is the only one I know by heart. Cast iron particles might be causing discolouration, but I am fairly sure there is a simple way to remove it.
How much is the bill they are trying on?
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