Jeanna,
I have dried all sorts of Zinnia's in silica sand and they dry wonderful. Make sure the bloom is not too old, and there is no moisture on it. The thicker the bloom, the longer it will take to dry.
I use a container like an old plastic ice cream container. Just place a couple inches of silica sand down first, then place the bloom face up, gently cover the bloom with silica, until it is totally covered. I would let dry in the silica for at least a week before you check it. Keep the lid on the container when drying. When you work with silica, make sure you use a dust mask. They make a wonderful wreath for fall using the fall colors, and other blooms and wheat.
I hope this was helpful! Wish I could have grown more this year, but we had a terrible drought here.
Good luck,
Julie

thanx julie! is the silica sand the same as silica gel?