Silica sand? Maybe it's similar to silica gel?

There's definitely more than one way to dry a flower, depending on the end result you want, says gardening expert Indrani Hawkins. She points out that the faster you dry a flower, the more color it will retain--with the exception of hydrangeas. She also notes that you'll get more shrinkage if you apply more heat. Here are Hawkins's instructions for several popular methods:

Silica Gel/Standard
Known as silica gel, this is actually a sand, and you can use it or substitute borax, cornmeal or clean sand:

Use a hat box to dry your flowers.
Put a thin layer of silica gel on the bottom.
Put the rose in.
Start building silica around the bloom, to support it so it's not crushed in the drying process.
Then, sprinkle more silica gel on top, as shown until the bloom is completely covered.
Put cover on the hat box, and forget about it for a week or so.
Come back and check it. If it's dry, take it out, and then use a little paintbrush to brush the silica from the petals. If it's not dry, put the lid back on and check again in a few more days.

Silica Gel/Microwave
To speed up the silica drying process, you can use the microwave, following these instructions:

Use empty cardboard egg cartons, with smaller blooms. For larger flowers, use a cardboard shoe box.
Put a little silica sand in the bottom.
Put in the flower, and then follow the standard procedure, sprinkling silica gel around all the petals until they're covered.
Close the carton or box, and place in the microwave.
Start with two minutes on low.
Pull out the still-covered box and let it cool for 5-10 minutes, so you're not handling hot gel or flowers.
Check to see if the flowers are dried yet.
If not, put back in for another minute or two as needed, cooling before you check for "doneness" each time.
Potpourri
To dry small blooms and petals for potpourri, Hawkins typically just uses her dehydrator. But if you don't have one, she recommends putting the fresh flowers in a basket that's large and has an open weave, and letting them air dry.

Glycerin
Hawkins recommends glycerin for preserving foliage in a way that keeps it pliable, not brittle. But, she warns, glycerin invariably turns leaves another color, so you need to simultaneously "dye" them green as you preserve them. Here's how:

Use two parts warm water to one part glycerin, in the bottom of a bottle or vase.
Put a "freckle size" sprinkle of green dye in the solution.
Cut the stems of foliage pieces and put them in the water solution so they can absorb the mixture.
If you have a large, thick stem (as you would with eucalyptus), crush it a bit with a hammer so it will have more of a "drinking surface."

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More ideas and recipes here:
http://web.hgtv.com/hgtv/web/searchResults?searchString=drying+flowers&site=HGTV&searchType=site

Common sand: Clean sand can be treated to produce a product similar to oolitic sand. Builders sand or play sand should first be washed thoroughly. Put the sand in a bucket of water with a couple of squirts of liquid dishwashing detergent. Stir it and pour off the water. Then, continue to add fresh water (pouring it off, adding some, etc.) until the added water remains clear. Then, dry the clean sand. For quick drying, it may be placed in a 250 ° F oven on a cookie sheet.