annealing pink gold

[Brian Hochstrat]

What is a good way to anneal 18k pink gold? Hauser and Miller, suggest holding it at 1200 for 15 min then quenching. Not an option for me, the closest thing I have to an oven, is a forge and it has two tempatures, hot and really hot. I tried heating it to various temperatures with a torch everything from about 250 deg to red hot, even tried cooling in different ways, water, pickle acid, air, (had no alcohol to try). All resulting in the same thing spring hard(its 22ga sheet and could only be bent with pliers), occationally I would get a soft spot but the rest would be hard. The green gold was easy to anneal and worked very easily, I can't figure out the pink. Any ideas? Thanks Brian
P.S. I will remember to order dead soft next time!

 

[DanM]

What size sheet are your trying to anneal? i have annealed hundreds of ounces of 18k red gold and i really can't think of anytime having problems with it. the way i have annealed it was with an oxy-acetelyne torch,large tip,reducing flame.coat with boric acid solution first,heat to a dull red,let cool to black and quench in hot pickle solution. a 1" X 3" strip of 18 guage could then be bent between opposing hands with no problems.

 

[TallGary]

Looks like 18k pink is naturally harder than some of the other 18k alloys. Here is a link to the Hoover & Strong mill products PDF that also has information on hardness and annealing.
http://www.hooverandstrong.com/pdfs/08Cat06Mill-Links.pdf

 

[Karl Stubenvoll]

That 1200 degree temperature is too high for a proper anneal. There is probably heavy oxidation of the copper in the alloy, and the grain size is much too large.

A reducing atmosphere is essential, and a reducing flame with an oxyacetylene torch will do the trick. Before heating, I dip the sheet of gold into a saturated solution of boric acid disolved in methanol, and then allow the solution to air dry on the sheet. Repeat to get a good coating of boric acid. Lay the sheet on a fireproof surface; flat charcoal surfaces work well as they don't draw heat away quickly. Heat the sheet as evenly as possible with a soft reducing flame and watch the boric acid coating---it will form a liquid, glassy coating at approximately 1000° F. Maintain that temperature for one minute and then quench the gold in water immediately. A hot pickle solution will clean off the boric acid and most of the oxides.

From the sound of your experiments, you are best off sending your pink gold sheet back to the refiner for a scrap gold credit. Sorry!

 

[Brian Hochstrat]

Karl, Sounds like a good method and I will give it a try, just one question what is a reducing flame? Brian

 

[John B.]

Hi Karl.
Thank you for the information. Couple of questions, please.
Where/how does one go about buying a small amountof methanol?
Can boric acid be bought at a drug store, jewelery supply or where?
Thanks, John B.

 

[Karl Stubenvoll]

A reducing flame has a rich fuel gas content. There is not enough oxygen supplied to the flame to allow complete combustion---an extreme example is the yellow sooty acetylene flame that leaves a black mess floating about if you completely close the oxygen line. No excess oxygen in the flame means a lower opportunity for the alloy portion of the gold sheet to oxidize.

Start with a neutral flame that has a proper blue core and then carefully decrease the oxygen feed until the blue core has a soft feathery appearance. This will be a good flame for annealing. Cutting the oxygen even more will result in a whitening of the outer flame---the flame will not be as hot, and there will be more soot to clean off.

Karl

 

[Brian Hochstrat]

Thanks Karl, thats great information. I really appreciate the help. Brian

 

[Swede]

Methanol: HEET or similar gas line anti-freeze from an auto parts store. It's cheap. Boric acid powder should be easy to find in a drugstore. There is also a commercial product called Keep-Bryte, which is a borosilicate powder that does much the same thing - it melts to form a glass-like coating on metal parts that are to be heated for annealing or any other high temperature process.

 

[jlseymour]

acetylene

I stopped using acetylene 30 years ago and went with Propane, much less oxidation.
The only thing you can't use the ruby tips in the mini torch. The mini torch usually comes with propane and acetylene tips, if not cut the ruby tip end close to the tip. You can also ream the hole for a larger flame...
JL

 

[jimzim75]

Hi Brian,
A simple method doing this is to use the boric acid and alcohol. Then use two large charcoal bricks.
Heat the metal to a dull red on one brick. Heat the other brick while doing this.
Once you get to the dull red just cover the metal with the other brick. Sort of a poor mans kiln.
You may have to do it twice or three times. As soon as the metal is cool enough to touch start again
with the heating. Don't quench.

 

[John B.]

Thanks for the answers to my questions, Swede.
John B.