Traces of Orange Color On My Newly Poured Gold Bar

[Ag and Au]

Hi All.... I recently poured my second gold bar, and unlike the first bar last year (which was bright, brilliant gold), this one has areas of orange discoloration that I wasn't expecting nor have I ever seen.

-- The material I used was PCBs and gold plated pins; I liberated the gold using the AP process.
-- I performed three (3) AR processes (using SMB for the drops each time) and five (5) HCL/hot distilled water washes at the very end.
-- The gold precipitant color was perfect. See photos 1 and 2.
-- I melted the gold inside a once-used crucible (only for gold), with less than adequate borax glazing, using two MAPP torches (video attached).
-- The first melt resulted in a brilliant color, but I was dissatisfied with the shape of the bar...so
-- I melted it again and had the same result....so
-- I melted it again and had the same result, but then I realized that the mold wasn't hot enough and I needed to pour it faster.

--Now comes my dilemma...on the 4th melt...I observed an orange color on the surface of the molten gold. Nonetheless, I poured it
and got a better shaped bar, but a strange orange color remained. See last three photos.

-- There is a piece of borax on the top of the bar. I have not washed the bar in diluted sulphuric acid yet.

Any thoughts?

 

[4metals]

Often slight discoloration can be treated by sprinkling just a pinch of niter (potassium nitrate) on the molten metal. I am not sure how this works with a torch melt but it is quite effective for crucible furnace melts. It is an age old technique called toughening. The niter oxidizes any surface impurities which will stick to the crucible wall as a bead of niter bounces around the surface sharing it’s oxygen with all base metal impurities it meets on the way.

 

[nickvc]

One way to avoid problems with final melt results is to change the reactants used when re refining fairly pure gold , if you have powder and decide it could be a better color is to change the method of dissolving it, there.are many choices here and come the time to precipitate your gold change the precipitant, for some reason which I’m sure a decent chemist could explain some elements can keep sneaking through the refining process especially with e scrap.
A single pass refine with mixed e scrap is almost guaranteed to produce less than perfect results, if you don’t believe me ask anachronism who only does e scrap and in large volumes.

 

[Ag and Au]

What puzzles me is why on the 4th melt the discoloration appeared?

 

[Yggdrasil]

What puzzles me is why on the 4th melt the discoloration appeared?

It must have picked up something.

 

[Martijn]

Hi All.... I recently poured my second gold bar, and unlike the first bar last year (which was bright, brilliant gold), this one has areas of orange discoloration that I wasn't expecting nor have I ever seen.

-- The material I used was PCBs and gold plated pins; I liberated the gold using the AP process.
-- I performed three (3) AR processes (using SMB for the drops each time) and five (5) HCL/hot distilled water washes at the very end.
-- The gold precipitant color was perfect. See photos 1 and 2.
-- I melted the gold inside a once-used crucible (only for gold), with less than adequate borax glazing, using two MAPP torches (video attached).
-- The first melt resulted in a brilliant color, but I was dissatisfied with the shape of the bar...so
-- I melted it again and had the same result....so
-- I melted it again and had the same result, but then I realized that the mold wasn't hot enough and I needed to pour it faster.

--Now comes my dilemma...on the 4th melt...I observed an orange color on the surface of the molten gold. Nonetheless, I poured it
and got a better shaped bar, but a strange orange color remained. See last three photos.

-- There is a piece of borax on the top of the bar. I have not washed the bar in diluted sulphuric acid yet.

Any thoughts?

Maybe you can wash it off in hot dilute nitric?
Nice bar by the way.

 

[Ag and Au]

I bet it was caused by foreign matter inside the crucible or perhaps by a "butane residue" from a torch that my employee used to glaze the crucible.
Either way, thanks for your input.