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How to freeze a credit card
Place the card in a freezer-safe container.
You may want to use a plastic storage bag, a piece of tupperware, or even a cup. Choose an item that will either cover up your credit card number or is thick enough that the number will not be visible through the ice.
If the number is visible through the ice, then you may be tempted to use the card number for online shopping. You could also cover the number with a paper towel or a small rag before freezing, but remember that it will be submerged in water.