How do I know whether or not something is safe for my fish?

I bought a cement gargoyle statue to put in my fish tank. How do I know if it's safe though? Since I won't get my fish for another 2 weeks, I was thinking I could just put the gargoyle in the tank now and test the water tomorrow to see if it changes anything. I rinsed it with warm water already to. So does that sound like it would be okay?
 
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