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18k gold finish


#1

I would like to know if anyone can help me with a question about
18k gold finishes. After casting and break-out my gold has this
great satin texture and bright yellow color, however after any
finishing, ie. sprue cutting and cleaning, I am un able to regain
that same original color and texture. I have tried sand and
glass bead blasting, but both produce a darker finish. I have
tried reheating pieces and pickling them, but still not the same
finish. I hope some one out there knows of a mechanical means,
maybe rougher sand for the texture, and/or a chemical means,(
bright dip) that works for color. Any help would be greatly
appreciated.

Kevin


#2

Hi Kevin,

After cleaning and finishing your piece, try this process. First
coat the piece in boric acid an metholated spirits mixture.
Anneal the piece until it just starts to go light red. Let it
cool down enough to be picked up with your hands (but still
warm).

Place in a warm mixture of hydrocloric acid and water. (Approx.
1 part acid to 3 parts water) temperature should be about 50
degrees celsius.

Remove after about 3 minutes and rinse in clean water.

I’ve used this process often with matt pieces and find it gives
a great colour. Hope this helps.

Regards.
Don
McLeod’s Jewellers-Goldsmith-Designer
Specialist in hand made jewellery & corporate gifts,
made to order in gold, silver and platinum.
http://www.mjgd.com.au
dmac@mjgd.com.au


#3

Hi

I am very interested in your post Re: 18k finish. Was this not
in response to a query on cast pieces? My question is whether
this process is also applicable to fabricated work? The light
red colour require after applying the methylated spirits & boric
acid is perhaps too hot?

I have been searching for some time for a method a bringing up
the fine gold to the surface of 18k gold. I’ve tried depletion
gilding through repeated heating,pickling (Sparex), brass
brushing but with little success. I’ve also read the article by
Charles Lewton Brain which contains various recipes which all
appear rather dangerous and or time consuming. I believe that
in Germany there is a product which is widely used for this
purpose. It is a powder which is placed in a crucible then
heated, becomes liquid. The piece is immersed in it and then
washed in water. I have no idea what this powder contains but
sounds similar to what you do - although there are no acids
involved in the latter.

I would be absolutely delighted to find out more about this. If
you have any more I would be most grateful.

Regards Christel
from West Australia


#4

Christel, In reply to your post, the process is as follows.

Saltpeter (Potassium Nitrate)    4 parts
Alum                                       2 parts
common Salt                           2 parts

Add enough water to make a thin paste.Place in a crucible and
boil. Place the article attached to a silver wire into the
mixture for 10-20 minutes. Rinse with hot water and scratch brush
with brass wire brush and return to the solution. Rinse again in
hot water, scratch brush, wash with soap and hot water, rinse in
hot water and dry off in sawdust. This will give you the high
karat colour you are looking for.

Best regards.
Neil George.