I am using wood slabs ( 2" X 9") for wedding centerpieces. I have a friend who will cut them 6 months early. He says that unless I wax them that they will all crack badly. What would I use to preserve them? Is this necessary? How would I best store 20 of them? Sorry, I don't know the type of wood (from Missouri) that he will use. I will be bringing them to Florida.
Paraffin is a low temperature wax (around 100 F) that is inexpensive and can be melted in a pot (or disposable aluminum baking pan) to allow dipping. Its brittle at room temperature, so your slabs must be handled gently after dipping.
It is best to dip just the end grain ends of the piece and leave the other 4 sides alone. Keep them out of the heat and sun, a root cellar would be perfect. (probably not an option in FLA). Perhaps a cooler, this will let them dry very slowly, a key to minimizing splitting.
It is usual to make the original piece a bit oversize and then mill it to the final size after it is dry. This is why a 2 x 4 is 1.5 x 3.5, a combination of shrinkage and final sizing.
This will allow you to trim the top and bottom so that they are parallel and will hold the vase steadily. A block plane or sander can make one side flat and a thickness planer will make the other side parallel to it.
My guess is that by wax they are referring to a finishing wax. It is easily applied and helps protect the finish against the environment, however it is not a durable finish so it is not appropriate for items that are handled frequently.
A quick search on Homedepot turns up a bunch of items, but you'd be looking for something like this: