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Gold finished surface


#1

I’m casting quite a lot in 18 and 22 kt. gold and am looking for a
finished surface that is glowing, rich and lustrous, like many of
the ancient artifacts I’ve seen, not ‘fresh of the buffing wheel
glittery’. I’m thinking that if I polish, then sandblast the piece,
with say a 50 micron grit, that might do it. Any suggestions?


#2

I get a lustrous antique look on 24kt and .999 Platinum by
polishing, then lightly hand buffing with a green Scotchbrite pad.
I’m sure it would also work on 18 and 22kt.

Karen Hemmerle
in windy Boulder, Colorado


#3
I'm thinking that if I polish, then sandblast the piece, with say a
50 micron grit, that might do it. Any suggestions? 

Most sandblasting grits will leave you with a dull matte surface,
not so lustrous. Glass beads might be better, as these leave a
sheen.

But I’d suggest, instead, a brass brush. get one of the very fine
bristle “platers” brushes, and use it on the polished surface with
some soapy water. Scrub in all direct lions. It will take off the
high polish, and leave you with a finely patinaed scratch brush
finish. Much higher sheen than any actual satiin finish, yet not
quite high polish either. If you do a lot of this, set up a wet
buffing wheel with pulleys to give you a very slow speed, like 300
rpm. You can do this with some lapidary machines if you change the
pulleys. Then you can use the rotary brass or nickel silver scratch
brushes. Same very fine bristles, and be sure to use them wet, with
soapy water, or the traditional lubricant, stale beer… (Really.
Not sure it’s any better, but it IS the traditional lube for a
scratch brush) Nickel silver brushes are better for white metals,
while the brass are better for yellow, since the brushes can tend to
color the metal a little.

Other finishes to consider are a matching color electroplate. The
plating can slightly dull down the high polish, and then you bring it
mostly back up with some baking soda on a finger tip or soft brush.
Looks very nice.

So does a bombed finish. The downside is that this one takes some
proper equipment/knowledge to do safely, as it’s using cyanide in a
manner not suited to beginners…

Hope that helps.
Peter Rowe


#4

We have used sodium bicarbonate in a blast cabinet for that muted
soft finish. I have also seen pieces that were picked in nitric acid
to bring out the yellow color. Are you blasting with flint sand or
glass beads. The glass bead when new will give your pieces a slightly
"burnished" look.


#5

I cast frequently in 22k, and 18k is the lowest karat I usually
cast. I understand what you are referring to.

18k generally will not develop the patina you desire, but 22k
develops this patina with wear, possibly a reaction to skin acids or
the atmosphere??? I have had some 22k pieces come back to me for
sizing, stone tightening and the like, and I’ve noticed a rich 24kt
like patina that disappears with buffing. Maybe there’s an acid dip
that will produce this patina. It does seem like surface copper is
oxidizing away, if that makes any sense chemically.

I have seen some pretty darn good looking 18k alloys from time to
time, and they do seem to develop the lustrous patina of 22k. The
high silver content 18kt alloys (greenish) never develop this patina.
I obtained some Hauser and Miller 18kt gold that has this property.
It was extremely difficult to torch melt cleanly. It seems that the
copper in this alloy reacts with oxygen (propane/oxygen flame)
producing greenish sparks during melting, the result being cupric
oxides and micro porosity in the melt. Using resistance melting
however produced excellent results. If the patina is producing by
the disappearance of surface copper, the high reactance of copper in
this particular alloy would account for it. Please note I am
uneducated in chemistry, so the explanation for this reaction could
be a result or interaction with salts, or who knows what.

I don’t understand the aging mechanism that produces a deep patina
on some high karat golds. I am hoping someone with the technical
skills will chime in here and explain it to us. I think if anyone
could figure this out, it would be the good folks at PMWest. Hello
Daniel…

Jeffrey Everett


#6

The surfaces of many ancient artifacts are depletion guilded. Heated
up and pickled many times leaving a fine gold surface. You can get
that soft look on this by using (I hate to say it) spit and an agate
burnisher.

Tony Konrath
Key West Florida 33040


#7

I do a lot of work in 22k and some in 18k. I like to burnish my
pieces. Not only do you get the glow that is rich, and lustrous, but
you get a handmade look, important on a cast piece. It is, however,
quite laborious. You can use steel, tungsten carbide, or stone tipped
burnishers. Soapy water helps. If the strokes are too much in
evidence, going over the piece with a paste of Bon Amie (felspar
powder) will bring down the shine. See my website for examples of
bunished finishes (especially the repousse section).

www.sumnersilverman.com


#8

Where can you purchase a nickel silver rotary brush?