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Marble and Oxalic Acid

Stone Conversations : Archive 1 : Message 00868

From: Walter Arnold <walter@xxxxxxxxxxxxxxx>
Date: Fri, 11 May 2001 08:25:15 -0500
Subject: Marble and Oxalic Acid

At 07:20 AM 5/11/01 -0500, Linda wrote:

Quoted text begins.I am in the process of polishing my first marble and I have a question. In
the book Direct Stone Sculpture by Milt Liebson, he says to rub on a
solution of oxalic acid onto the sanded marble before applying either tin
oxide or wax as the final finish. He gives no explanation as to why one
does this on marble only. Also the other sculpture books I have do not
mention this step at all.
Can anyone explain what the purpose of oxalic acid is?
End of quote.


The acid is one stage in the polishing process. It takes the marble a bit
smoother than the sanding does, and smooths out the microscopic grooves
left by sanding. You need to flush the surface thoroughly with water after
rubbing in the acid solution, or bits of acid will remain in the pores of
the marble and slowly eat away, living tiny pits.

Mix the oxalic powder with a bit of water to make a paste, dampen a piece
of cheesecloth with it, rub till you feel it start to bite into the stone,
and then really rub for a while till you see the surface is very smooth.
Then give it five minutes, and wash thoroughly.

Walter S. Arnold * walter@xxxxxxxxxxxxxxx

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