Is it better to use natural tortoise shell or copper tortoise shell for divination?

I want to calculate hexagrams, but now I can't make up my mind whether to buy copper turtle shells or natural real turtle shells. I want to buy a real turtle shell on Taobao, but I'm afraid its shell is not cleaned and the remaining turtle meat has an odor. Secondly, I'm afraid the turtle's death will not affect the calculation. Third, whether the turtle shell will still carry germs and bacteria. How about a copper turtle shell? Everyone give me a suggestion, thank you.