Teri, what do you mean by "white iron"? Is this wrought iron painted white?
Assuming that it is, as long as it is not rusty or heavily rusted, anyway, there is no reason to sandblast.
Are you sure that the "white iron" or wrought iron is really that or is it square tubing bent and welded together to look like those?
And is your "brass" really brass or is it plating on steel tubing? Can the bed be disassembled to get the "brass" pieces off and what is their condition? A magnet will stick to steel but not real brass, however because the magnet would be attracted to most iron or steel materials that were close to the magnet too.
Teri, we need a lot more info to determine a direction. We will try to help if we can.