Sizing advice: First check to see if your paper already has sizing. Many high quality watercolor papers do. If so, this is generally enough. Van Dykes and Kallitypes definitely need sizing. Arrowroot is a very, very safe sizing. They make cookies for babies out of it. But it's not the most effective method. Better choices are gelatin, gesso or gum arabic. Get Christopher James' book "The Book of Alternative Photographic Processes" for the skinny on everything you want to know and more.