These are sand dollars from the gulf coast. I found them in Port Aransas, Texas.
This is the color they are in their natural state. Many people prefer their sand dollars to be white instead of their natural color.
First, put the sand dollars in a bowl and pour water in a bowl just enough to cover the Sandollars.
What them so for around 30 minutes and change out the water Half way through.
Don't worry if they float for a couple of minutes they will eventually sink.
Next put one part bleach and three parts water into a bowl and let the sand dollars sit for around 15 minutes or until white.
But the longer you have them in the bleach and water solution , the weaker the sand dollars become.
Rinse the Sand dollars thoroughly and allow them to dry overnight on a paper towel.