why did my fake gold material turned silver and then after a week, it turned gold again?

Question

we used baking soda and coke for this. this is for our investigatory project for science. thanks :)

Answer 1

Your baking soda and coke stripped off the top, thin layer of metal (brass?), leaving base metal underneath. But since this was very clean, it oxidised over the following week. It's now "tarnished", so it looks gold again.