Cleaning ceramic floor tiles

I would appreciate receiving advice on how to clean ceramic floor
tiles in a house in France.  They are about 50 to 75 years old and
do not appear to be glazed, although it is difficult to know what is
hidden under the grime. I have heard reference to caustic soda
(sodium hydroxide?) and muriatic acid for this purpose.  Are these
recommended?  If either is, what health and safety precautions are
suggested.

Ellen Desmarais
Ottawa, Canada
613-745-7517
Fax 6l3-745-7417

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                  Conservation DistList Instance 12:58
                 Distributed: Friday, January 15, 1999
                       Message Id: cdl-12-58-016
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