Marble and Oxalic Acid

["Simon Brown" <moonsong@xxxxxxxxxxxxxx>]

Hi Linda,
Oxalic acid reacts with the calcium carbonate in the marble to produce
calcium oxalate on the surface, which smooths the marble finer than any
abrasive could. This chemical reaction assisted by heat and friction from
you rubbing the acid paste in by hand or machine brings the marble to a
brilliant shine. I have read that acetoacetyl has the same effect, but I've
never tried it.Oxalic acid comes either crystalline like sugar or as a liqid
in a tin, I think Tenax supplies it in a liquid form.

Tin oxide is a very fine abrasive used to polish granite. It can also be
used on marble, sometimes combined with oxalic acid. Tin oxide comes as a
white powder like flour, and if you are using it on a dark stone, mix some
synthetic iron oxide with it to colour it the same as the stone. If there
are any pits or microcracks in dark stone,  white tin oxide gets caught in
them and stands out, so colouring the tin oxide helps to hide any residue
you can't remove. Lead monoxide can be used instead of tin oxide- I've never
tried it, and I think there could be a health risk from the lead. Years ago,
masons used to polish granite with a lead plate and tin oxide. Now there are
many types of diamond compounds for polishing, lead plates aren't used (to
my knowledge).

Oxalic acid is chemical polishing
Tin oxide is mechanical polishing

Whatever way you polish the most important part is the preparation. The
surface must be smooth, free from scratches and honed to a dull shine before
you can start polishing. A piece of folded hessian or a camel-hair pad is
good for hand polishing, camel-hair pads for machine polishing. If you use a
machine to polish a surface, you must take care not to run the machine too
fast or hard or it will scorch the surface and you will have to start all
over again.

Oxalic acid will also etch any polished surface it is left on, so you must
take care not to let it dribble down the sides of your workpiece, and rinse
it really well afterwards. Get organised and work quickly and cleanly, in
other words!

Oxalic acid reacts with the calcium in your bloodstream too. Calcium oxalate
builds up in your kidneys as marble crystals- kidney stones! Take care when
you use it, it's absorbed through the skin.


for some more info.
Regards,

Simon Brown

----- Original Message -----
From: Linda