This is a wonderful thread, but I still have a question -- I know muriatic acid is highly corrosive, especially for metal. Is this a problem for a sign with some loss of porcelain? Will using muriatic acid further corrode the rust spots where porclain has been lost, or cause a loss of more porcelain on that part of the sign? Does washing it off well with water take care of the problem. Again, any help would be appreciated. This is really a great site for assisting the novice collector. Thanks.