Baking soda is the best household item you can use to get the accumulated gunk off your old bathtub. Mix two parts of baking soda and one part of hydrogen peroxide in a small glass bowl. Apply this paste on your enameled bathtub or sink and let it set for about 30 minutes. After half an hour, give your tub a good scrubbing until all the stains are gone. Rinse it well with normal water.
Cream of Tartar
Cream of tartar is also used with hydrogen peroxide to remove the tough stains from a bathtub. Make a thick paste of cream of tartar and hydrogen peroxide by mixing the two in a small dish or bowl (add peroxide drop by drop). Coat the bathtub stains with this paste and leave it to dry. When you will remove the paste, you will not find any traces of those hard stains.
To remove the yellow spots in your enamel bathtub, use a mixture of salt and turpentine oil. Mix salt and turpentine in equal parts in a small bowl. Wear thick rubber gloves and rub this paste on the yellow spots until they are gone. Rinse the tub thoroughly and pat dry using a washing cloth.
Sometimes a stubborn stain around your white porcelain tub becomes impossible to remove. All that you need to cut this stain is an oven cleaner. Spray the oven cleaner over the stain on your porcelain bathtub and let it set for a few hours before you give it a thorough rinsing. However, never use oven cleaners for a coloured porcelain bathtub, since they can cause it to fade.
Vinegar is also effective in bringing back an old porcelain bathtub's shine. Scrub your bathtub thoroughly with full-strength white vinegar and rinse it with cold water. To remove hard water stains, add three cups white vinegar under running hot water and leave it for four hours. Drain the water and scrub off the stains.