Is it important to varnish or clear finish polymer clay or its substitute?

I am going to make coffee beans with polymer clay. And if I don't get polymer clay in the market, then I am going to make a substitute of it by using cornstarch, stearic acid, citric acid, glycerine, Vaseline and PVA wood glue. After that I am going to use acrylic paint to color the beans. And I am probably going to bake it too.

In both cases, should I use varnish or clear gloss to make them look real and obtain longer durability? Or is varnish just going to ruin the clay or clay substitute?

Please help!