This section is from the book "Cassell's Cyclopaedia Of Mechanics", by Paul N. Hasluck. Also available from Amazon: Cassell's Cyclopaedia Of Mechanics.
To clean white marble that is much discoloured, make a thin paste with fuller's-earth and water to which has been added 25 per cent, of Liquid ammonia. Spread this over the marble with a brush, allow it to remain twenty-four hours, then wash off. If all the stains are not removed, repeat the operation.
 
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