The yellow or brownish ring that forms inside a bathtub is from the effect of hard water on soap. When wet, it rubs off easily but when dry, it is hard and nearly insoluble. It can be removed with a solution of oxalic acid in water, applied for convenience with a dish mop. Javelle water will also take it off.
Enamel will chip when suddenly heated. Enamel around the outlet of a sink may chip with the sudden turning on of very hot water when the sink is cold. Chipping is caused by the sudden expansion of the iron; the enamel will not chip when heating is so gradual that enamel and iron expand together.
Broken enamel on a drain board, the rim of a sink, or other place not exposed to standing water can be patched with materials under such names as bathtub enamel, liquid porcelain glaze, enamel patching putty. The method is to fill the broken place to the level of the surrounding enamel and to finish with a glaze. The broken place should first be washed with benzene to remove traces of grease and soap, and then the exposed iron rubbed bright with fine sandpaper. After another wiping with benzene, the material is applied according to directions on the label. (Be careful of fire when using benzene.) The patch should be protected against water and rubbing until it is so hard that it will not dent with pressure of a fingernail. The patch is then smoothed with No. 0000 sandpaper and coated with glaze for waterproofing. Chipped enamel in a sink or tub in a position exposed to standing water cannot be patched: there is no material that will not soften eventually.
Toilets are usually made of solid porcelain or pottery for maximum protection against leakage. Cracks in a bowl of either of these materials cannot be repaired; the toilet should be replaced.
A crack in a solid porcelain flush tank can be kept from leaking by cleaning and drying the inside surface and then applying an epoxy resin, such as Devcon or Masonweld, to the crack. The epoxy must be forced into the crack, in order that it may make a bond with both sides of the opening. An ordinary kitchen knife is satisfactory for forcing in the epoxy, but it will work better if the blade is immersed frequently in the special solvent supplied by the manufacturer for cleaning tools and removing excess material before it sets.