Kim,

Having many years of experience in cleaning decorative arts silver
collections for exhibitions I can offer some thoughts in response to
your query.

First of all, silver is a soft metal (about 2.5 moh hardness) and
because of the nature of how historic silver was fabricated through
hammering, fire anealing, pickling, and polishing, there is often a
thin veneer of highly finished surface on top of oxidized "Fire
scale". Aggressive polishes and chemicals can not only refinish the
original polished surface but it can also etch and erode right into
the underlying fire scale, leaving darker globular shadow-like areas
on the surface. If you have Sheffield Plate a similar thing happens
with the fine silver plating being eroded exposing the copper plate
beneath. Also, historic silver has often been through cycles of
polishing so it is common to see years of old polish residues built-up
which also can be a source of corrosion.

So you want to use a polish that is hard enough to gently remove or
reduce the tarnish but will not be so aggressive as to have
detremental effects on the historic silver surface.

This is why conservators recommend using a self-made polish from
precipitated chalk (precipatated calcium carbonate - usually found
from chemical suppliers such as Fisher scientific in Atlanta, GA or
from conservation suppliers such as Conservation Support systems in
Santa Barbara, CA) that is mixed into a paste slurry with distilled
water (tap water contains chlorine which is very detrimental to almost
all metals). Another product that is also acceptable, and is also
available premixed in 6 oz.bottles , is 0.05 deagglomerated gamma
alumina micopolish II (# 40-6365-006) available through Buehler corp.
It is used for fine metallographic polishing for micorscopic
examination.

But before polishing you should wash each piece in a bath of distilled
water and a non-ionic detergent to remove dust (most household dusts
are abrasive and can scratch silver, never-ever wipe off dust with a
rag on historic silver objects).Some detergent additives for
non-spotting of glass in dishwaters are non-ionic, just read the
labels carefully - or if ordering from a conservation supplier get a
small quantity of Triton XL-80N detergent - only a few drops are
needed. You can use a soft natural bristle brush gently to remove all
of the dust, and then a final rinse in straight distilled water.

These polishes should be applied with either clean cotton cloths or
cotton q-tips (You will be wearing clean gloves too, won't you?
Fingerprints will tarnish and etch right into the metal).You can clear
off the area you polished with a clean cloth and continue. Make sure
to leave the tarnish and buildup in the recessed of the chasing and
engraving as this is considered patina. Also be very careful when
polishing small projecting elements, solder joins, lids, handles, etc,
as these can easily become damaged by handling and/or polishing. If
you have wooden handles then they either have to be carefully removed
and the metal treated sepearately or you have to treat them in a way
so as not to get with the polish or the water in contact with the wood
or ivory insulators that are commonly found on historic tea wares, for
example. When you are done, rinse the silver in a bath of distilled
water and a non-ionic detergent and natural bristle brush and rinse in
clean distilled water. Wipe the silver with dry clean cotton cloths
and use a hot air dryer to remove excess moisture that may be caught
up in the recesses and interior. Make sure that the historic silver in
only in contact with non-acidic materials while either on exhibit or
in storage.

That is the best that I can recommend to you without actually being
there - I and some of my conservator colleagues have offered silver
polishing workshops in the past, and this is the absolute best way to
learn about the materials and techniques to safely polish historic
silver. So you might want to contact a nearby metals or objects
conservator (I believe that there is also a regional lab near you in
Oberlin) and perhaps bring them out for a day to train you and
volunteers in doing this.

Cheers!
Dave

David Harvey
Conservator
Los Angeles, California USA

On 10/31/05, Kimberly Kenney, Curator <[log in to unmask]> wrote:
> Hello all,
>
> I will be putting some pieces of silver on exhibit in
> the next few weeks.  In researching how to clean the
> tarnish (which I am only planning to do to the badly
> tarnished pieces), I found a recommendation to use
> "washing soda" and distilled water in Bruce MacLeish's
> book _The Care of Antiques and Historical
> Collections_.
>
> Can someone verify for me what "washing soda" is?  And
> also, where does one find "precipitated chalk"?
>
> Thank you,
> Kim Kenney
>
> Kimberly A. Kenney, Curator
> Wm. McKinley Presidential Library & Museum
> 800 McKinley Monument Dr. NW
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