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Oxidation on satin finishes


#1

Hello,

I have been having a problem with some…not all of my satin
finished peices…mainly the gold- filled. I prefer the satin, or
matte finish to shiny, however, I have been noticing that the
gold-filled peices oxidize very fast. I have been putting a laquer
over them but this only works in some cases and after about a week
the beautiful finish will have dissappeared and the peice will look
old. This does not happen as often with the silver. I have also
noticed that if I try to polish the peices with a polishing cloth it
only makes them look more drab, therefore needing to be re-polished
with a buff wheel. This however does not help my customers because
they have no access to a polishing machine. Does anyone have any
suggestions??

Laura


#2
 I have been having a problem with some...not all of my satin
finished peices..mainly the gold- filled. 

Laura, the first thought I have is that normally, a gold surface
shouldn’t oxidize all that fast. Even as low as ten karat oxidizes
only slowly in most cases. So that makes me wonder if in processing
your work, you’re actually buffing or polishing or satining, or
whatever, right through the actual gold layer on the gold fill, and
have exposed the underlying base metal. Doing that would make the
metal behave as you describe. Test it with a small drop of nitric
acid. If it bubbles up green right away and actively, then this is
what you’ve done. The fix, of course, is to be much more aware that
the gold thickness on gold fill is quite thin. You can’t do all
that much finishing to it without risking cutting through. A light
satin finish should be fine, as is normal buffing with rouge. But if
you’re first needing to significantly buff with tripoli or even
sand out deeper scratches or tool marks, you could be in trouble…
Another possibility is that if, in soldering the gold fill, you get
it too hot, you can get diffusion of the gold into the base metal,
and the base metal to some degree up into the gold. That can increase
the percentage of copper in the surface, essentially lowering the
karat. Suspect this if, after soldering, you’ve got significant fire
scale or discoloring. Generally, use only easy solders, or solders
made especially for gold fill, when soldering the stuff. In either
case, remember that the base metal used for gold fill is chosen in
part to match the color. It is not always super obvious when you’ve
cut through or otherwise damaged the gold layer, when the metal is
freshly polished or finished, as the underlying bronze or brass or
whatever is very close to the same color.

Peter


#3

Hi to all,

Everyday I read the postings with interest. Thanks to Ganoksin for
the forum and everyone for their useful contributions.

I share Laura’s preference for satin and matted surfaces. They can be
used to great effect but are very hard to clean and keep clean.
Rubbing satin or matted surfaces whilst cleaning, only helps to
polish the metal, which defeats the whole effect.

I use matted surfaces a lot in my jewellery and can sympathise with
your problem Laura.

Four suggestions follow

In the past I used chemical dip containing thiourea to remove the
discolouration but found that it could only be used on pieces set
with hardy stones. The acid in which the thiourea is dissolved causes
major damage to the surface of chemically reactive gems. Thiourea is
also poisonous and regarded as a possible carcinogen by some. The
thought struck me that ionic reduction cleaning would probably be the
answer - it was. So that is what I use. It is a remarkably useful
tool in keeping jewellery clean in general, but satin or matted
surfaces in particular. The process has two added spin offs. One is
that the process is safe on pieces set with delicate stones like
pearl, coral, opal, turquoise, lapis etc. The second spin off is
that millions of hydrogen bubbles are formed on the surface of the
metal. These have the effect of scrubbing and loosening bits attached
to the surface of the metal. By the nature of how they are formed
they have the ability to lift bits left deep in the matted surface.

I know ionic cleaning has been around for some time but it has never
struck a chord and become mainstream and part of every jewellers
toolkit; it ought to be! I was so impressed with the effectiveness
of electrolysis for cleaning metal surfaces that together with my
son, an Electronics Design Engineer, set about designing a simple and
versatile unit of our own. We now manufacture and sell these units.
There are of course other manufacturers of ionic cleaners, have a
look on the net. Electrolysis works very, very well, give it a try!

Two further suggestions Laura, make sure that you thoroughly
neutralise the pickle with bicarb and wash the surface thoroughly in
deionised or distilled water. Some tap water can contain sulphur and
other minerals which can discolour the surface. Secondly, some
lacquers set by a chemical reaction which can liberate substances
which discolour metal. You will also loose that attractive matted
surface once the varnish is applied, so it isn’t the best solution.
If you go the way of ionic reduction cleaning, you will be able to
easily apply an invisible tarnish inhibiting layer by electroplating
the surface with sodium dichromate. One word of caution though, this
substance is slightly acidic and cannot be used on pieces set with
chemically reactive stones. Ionic cleaners are very simple to use
and inexpensive to buy and run. They can be recommended to customers
so that they can safely clean their own jewellery and keep it in
pristine condition. You could even offer your customers a free clean
as part of the service. Hope I have been of some help Laura.

If Ganoskin will permit me, our units can be seen on our web site
www.jcr-engineering.com or www.calvertjewellery.com.au.

Regards to all,
Cal.


#4

Laura,

I’m not sure if this will solve your problem or not, but you could
try sending small pieces of the fake “scotchbrite”- the grey stuff
sold by the sheet by Rio Grande with your orders to stores. I manage
a retail jewelry store in Santa Monica and the salt in the air
causes all of our sterling jewelry to tarnish quickly and we’re
constantly polishing. Some of the items we carry have a matte finish
and this is how we polish them while retaining the matte finish. I’m
assuming that other stores polish their stock on a regular basis as
well.

We also provide tiny squares of the stuff to our customers when they
purchase any matte or sandblasted jewelry.

Good luck,
Amery