Marks of graphite, (primarily a lubricant) Cannot be erased without a trace. Perhaps without a trace to the naked eye, but under magnification and the correct light it would be detectable. It is altered regardless if detectable or not. There are those that say it is ok. I think it is altering the card. There are also those that think soaking in H2O is ok to clean, this is wrong. When a card is soaked the ph of the paper is changed unless other chemicals are added, making it prone to rapid pyrolysis. Upon testing, soaking can be detected also, it is another kind of "altering" that some accept, I do not.
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