I have a cast iron bathtub that has been enamaled. There are certain spots were the enamal has worn off and the tub has started to rust. From the advise of a clerk at a hardware store i used a porcelain touch up kit to treat the worn stops. It looks messy and it has bubbled in areas where the porcelain meets the enamal. Is there anything else i can do to fix this mess? Should i have used an enamal spot kit? It also is the color of a washed out white!