You may have to sacrifice one to save the other. Put a groove in the bottom edge of the lower one with a nail file, then tap FIRMLY on the bench to shatter it. If you are holding the top one, it should be unharmed. A teatowel on the bench may help corral the shards for disposal. Rubber gloves as per StudSpud’s comment are a very good idea.
You may have to sacrifice one to save the other. Put a groove in the bottom edge of the lower one with a nail file, then tap FIRMLY on the bench to shatter it. If you are holding the top one, it should be unharmed. A teatowel on the bench may help corral the shards for disposal. Rubber gloves as per StudSpud’s comment are a very good idea.