1981 scratch offs help

Got my son some 81 scratch offs for his birthday and I find that when scratching them off the word under is gone... I am guessing the age of them has compromised them. Any suggestions on how to possibly scratch the black without also taking away the out or hit underneath? This could be really fun only if!!!!
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I have an unopened box and I'm tempted to see what happens ---
Is this happening on every dot on every card?
Seems odd
Erik