There are a lot of sealants out there and not everyone is able to get the almighty Mister Super Clear, so here is a list of sealants and whether or not they can be used, according to DoA. Always remember to use a "matte" or "flat" product unless you want your $600 doll looking like Barbie's giant shiny cousin.
DoA A-OK -> (in order of awesome) Mr Super Clear Matte/UV Cut, Model Masters Lusterless (flat) Lacquer Overcoat, Mr Top Coat Matte, Testors Dullcote.
Questionable -> Citadel/Games Workshop Matte Sealer/Purity Seal\\, Windsor & Newton (matte whatever)\, FolkArt/Plaid matte\, Micador matte?, Crystal Kote matte?, Americana matte?, LusterKoat matte?, LUKAS SPRUHFILM matte?, Grumbacher's matte?
NO WAY! -> Krylon Matte, oil based anything!, workable fixatives, stuff with acetone in it.
Yay! -> Liquitex Acrylic Paints, Chalk Pastels, PrismaColor Pencils.
Mebbe? -> regular pencil\.
Nay! -> oil based anything!, sharpie, pen, dark nail polish, Hobby Colour Clear Gloss.
Yes! -> Volks Cleaning Sponge, Mr Clean Magic Eraser, gentle dishsoap and water.
Uh, Maybe? -> acetone nail polish remover?\^?*, baking soda, toothpaste.
No! -> bleach, oil-based anything!, colored nail polish remover.
*There has been a lot of debate over whether acetone = bad, so to be on the safe side, I recommend not using it. If you do use it, rinse very well and often with water and wash doll afterward to remove residue.