The last three pieces of silver that I’ve heated (with the dual
goals of both annealing and raising the fine silver) have developed a
strange grayish (with the slightest hint of yellow) color. This is
unlike the usual “frosty” appearance that I was hoping for (and
usually get). This is only the on the side of the metal exposed to
the flame (not on the underside).
I’ve never encountered this before. I cleaned all pieces very well
before heating. I mixed a fresh batch of pickle; I also pickled for
longer than I normally would. Does anyone have any ideas on what I’m
doing wrong?
Thanks in advance…
Sometimes mixing “extra strong” sodium bisulfite pickles (pHdown,
sparex, etc.) will leave a film or discolour the material, as will
using a brass brush (why anyone ever uses brass to clean gold or
silver alloys has always remained a mystery to me; it’s like
embedding micro-scratches of base metal into a piece! anyway). It is
generally from an element in the alloy (sterling) that reacts with
the heat and solder and/or flux- particularly solders containing
zinc oxide…there is a reaction between the chloride and the oxides
that happens when heating the metal and chemically staining the
piece- also base metal contamination in the cleaning of the pickle
pot, flux applicator, or a million other insidious little traces of
base metals affect a piece or two though one before may have come out
just fine.
I always tell students never to use brass brushing (a.k.a. “scratch
brushing”) to clean any precious metal jewelry that is alloyed with
copper, even argentium…other jewelrs have also concurred that the
brass brushing is like introducing a contaminant to an otherwise low
risk operation…If you feel you must clean with scratch brushing use
a scotchbrite pad in any grit that you like, or a “no-rust"soap pad,
pumice slurry on a bristle brush (without the aluminum ferrule!) or
3M’s radial bristle discs in the pumice grade on a polishing or
grinding motor as they come in sizes up to 3” (perhaps 6" too, I
can’t remember) and do the job quickly on metal sheet or any
workpiece…
Then to remove the stain, whether firestained (from not fluxing well
enough, a contaminant, poor refinning of scrap, a bad batch of grain
or mill product from a refiner or vendor, etc.) or due to any number
of other reasons sandpaper, wet-or-dry papers, 3M micro-films
(Tri-m-ite is the 3M brand name for its ultra fine quality fiilms and
papers) or a nitric acid dip will remove it. To make a stripping
solution of nitric acid, add 5 parts water to one part nitric acid,
and heat in a clean glass or crockery vessel (without any chips,
interior glaze holidays, or hairline cracks whatsoever) to about
125-140 do not boil.
just a hotplate or slow cooker gives enough heat to make it
effective, or rather more effective than at room temperature.
Remember to neutralize it before you dispose of it, (though it will
last covered in a chemical resistant container for quite a while
between uses) That should brighten it easily, if you have any
objection to a dry sanding, or a paper or film cleaning- then you can
recheck your pickle on a scrap of metal and before using it again,
adjust the water to chemical ratio if necessary. rer
I thought that it was etched either from long pickling or strong
pickling. Light sanding and then buffing will bring back the silver
look.
marilyn
Please do NOT add five parts of water to one part nitric acid.
Please add the acid to the water.
Thanks you.
Jay
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