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Casting question: Dull, dark sterling silver


#1

Hi folks,

I was wondering if anyone else has ever experienced this or may have
some insight as to what has happened.

I recently got in an order from my caster in sterling silver. Most
of the pieces in one particular style came in a shade darker, or
more “grey” than usual. Also, the silver looked slightly more dull,
and not as shiny as all previous/other castings. I tried the
following, thinking perhaps it was just tarnished or not polished to
a high shine: tumbling in steel shot with burnishing compound,
several polishing wheels, buffs, various polishing compound,
etc…etc…and nothing, absolutely nothing helped. Sterling silver
still remained ever so slightly darker and duller. It’s not even
something you notice until you hold it up to a piece that is bright
and shiny.

Sending the pieces back to the caster to be recast, but after
speaking with them on the phone they don’t seem to have a clue as to
what was going on, and their logs did not show anything out of the
ordinary… Just trying to understand what might have caused this
inability to polish silver toa high, bright shine. The funny thing
is, the castings came out incredible as far as surface imperfections,
porousity, pits…there was not one in any of those pieces! It’s the
best looking lot in that respect. I am just baffled!

Thanks in advance!
Liz


#2

Sounds like there is a problem in the alloy or a reaction to the
mould material ( some moulding compound/ rubber contains suphur that
can react though usually ( and by usual I mean though it rarely
occurs, when there is a reaction at all the most common is…)
sulphuric compounds will yellow as opposed to greying ). The bottom
line is if the colour will not hold a polish and tumbling in shot
with burnishing did not work there is a problem there shouldn’t be
any colour difference in castings in the same lot if the casting
house uses. 925 silver not scrap ( i am wondering primarily, about
the source of the metal used: for instance, if you submitted scrap a
bit of solder in a pour could contaminate the lot), If they are
reputable and do this regularly, there will never be any differences
in the metal’s colour or castings from batch to batch whether you pay
extra for finishing or not it should appear uniform from lot to lot
). The only other thing that I can think of is that the pieces were
left too long in pickle therby degrading the alloy particularly if a
master alloy including a deox agen, or zinc was added to the crucible
either intentionally or unintentionally - but keep in mind wht I
interpret is that you have a lot of X number of pieces of which some
are shiny and “normal” in appearance and others are dull grey and
won’t hold a polish whatsoever.

I would first XRF test the lot to insure the purity of the alloy and
its composition from piece to piece - again, there shouldn’t be any
colour differences noticeable. - Ask a friend or precious metals
dealer to use his/her gun for a few moments to get an exact reading
of the composition. If it is the same from piece to piece that bears
on their responsibilties in making the job right. After you discover
the results include a memo to the casting house explaining the
alloy’s composition was different within one lot and that it should
be their responsibility to recast the original design, in the same
mould ( most casters keep clients moulds particularly when
flawless!) and ship it back to you at no cost to you. They should
definitely redo the job abd pay all expenses related to your return
of the pieces and the posting to get it back to you correctly- as you
initially contracted for. However, if you submitted your own scrap,
or pre-mixed alloy for the casting house to use then it is their
responsibility only to recast the pieces and regarding shipping
return them to you by whatever method you paid for originally…If
there is a problem with the metal they used from their vendor, or it
is that they tried to use scrap without your knowledge ( as I
presume you paid for what you expected to be “new” clean silver alloy
as opposed to “recycled” raw materials) but you are willing to give
them another go at it due to the quality of their mould making they
demonstrated in successive orders make them aware of the
unacceptability of the metal, be certain upper management is aware
of the entire issue and follow up after you receive the recast
pieces. I had a student reccently that was having his work cast by a
small “professional” casting house he found on the internet that it
turned out was using reclaimed scrap being purchased from small
independent jewelers and students that didn’t know enough to seperate
soldering mistakes from the scrap - and the professional casters were
also, it turned out students with access to rapid Prototyping
equipment used in a dental lab to make the moulds- so neither had
much experience- but their prices were cheap and they appeared to be
a “green” business- in the long run ( in this case after, 3
problematic orders ) it is best to know the business you are dealing
with and their reputation… It is generally best to deal locally
where possible or with an established company…other jewelers or
metalsmiths will generally give you all the reccomendations or
criticisms of a particular business you desire and then some… I
myself like becuase their metals always remain consistent and year
-to-year the colouration is the same ( unless they specify a change
in a material’s formulation), the turn around is fairly swift they
take care of any problems readily, and in terms of pricing they have
always been lower than the competition on small runs in
particular…( i have no affiliation with them whatsoever)…rer


#3

I would suggest that a slightly different set of conditions were used
for casting, the metal or mould being hotter, cooling rate being
different or other conditions that changed the microstructure of the
finished pieces. you wil really only tell by sectioning Quoting Liz