24k gold flakes turned black in lye solution

[RoseJoy]

Hi There

 

I make cold process soap and use a lye solution to saponify the oils. I made a batch yesterday and added 24k gold flakes. They have all turned black. Is it possible for the lye solution to affect the gold in this manner? I have checked with my supplier and they are 24K. I am not sure how to avoid this. Any help would be appreciated!

 

Thank you

 

RoseJoy

[frosch45]

Hmm, gold is extremely unreactive, however, lye, sodium hydroxide, is extremely reactive. It can easily react with many metals, and I think what happened is that the NaOH (sodium hydroxide, lye) reacted with your gold to make [ce]Au(OH)3 [/ce](gold hydroxide).

 

Gold hydroxide is usually a darkish brown.

 

It is possilbe however, something else happened. The gold might have catalized a reaction that would not have normally happened between some of your "ingredients".

 

One thing that you could do to test what is happening is put a gold flake in a small amount of lye solution on its own and wait for a little bit. See if the same thing happens to your gold flake, then I would guess that it is probably gold hydroxide.

 

By the way, where did you get your 24K gold?

 

 

And, if it is gold hydroxide, there is not really anything that you can do from stopping this reaction from happening apart from coating your gold with teflon or some rediculous and outlandish act. You could use something besides sodium hydroxide though. I'm not familiar with soap making, but if you know of another way to make it using different chemicals that aren't so corrosive, maybe that would work.

 

However, gold hydroxide is not very stable, and it decomposes when exposed to light. If your soap is already set (again, i'm not very familiar with soap making) and no more raw sodium hydroxide will be exposed to your gold, try putting it around noon out in the sun. It may take quite some time, but you may notice some general improvement (this also depends on how light-impervious your soap is).

Edited August 13, 2008 by frosch45

[John Cuthber]

Gold is perfectly immune to the effects of NaOH.

I can't think of any way that gold would be oxidised to Au(III) by soap and lye as Frosch45 sugests. If anything I would expect soap to reduce Au(OH)3 to the metal.

I also can't think of anything that would be in any normal soap that would affect gold. My best guess is that the "gold" isn't gold.

 

Perhaps you should ask the supplier to explain why his "24K gold" is affected by soap.

[frosch45]

I do agree, gold is very resiliant, and it is suprising.

 

You didn't heat the solution, did you?

 

maybe the sodium hydroxide was molteon

[RoseJoy]

ty all for the quick responses. I cut up my soap log and the gold that is in the centre is just fine. I contacted my supplier and it is 24k gold flakes used in cake decorating. the only ones that have changed colour seems to be the ones on the outside. could it have something to do with the air?? the lye and the oils are both combined at a temperature of 95 to 100 F. I didnt think that would affect the gold. This is such a mystery to me!!

[frosch45]

There is less than a .001% chance that it had something to do with the air. Gold is extremely hard to oxidize, so there is almost no way that the air would have affected it.

 

Who exactly was your supplier?

 

And I'm sure that I can speak for all of us in saying that we love science, and we are happy to help.

[hermanntrude]

i suspect what has happened is the physical structure of the gold flakes was somehow affected by the process, making it thinner and hole-ier. Finely divided metals often look black.

[jdurg]

Either that, or the gold exposed to the air attracted something to it that "stuck" onto the gold and the lye attacked whatever got physically, not chemically, attached to the gold

[hermanntrude]

of course. It could be self-assembly. anything containing sulfur would stick to the gold. It's not a chemical reaction as such but a strong bond is formed despite that. Never known it to turn the gold black, though... but I always used controlled conditions and small molecules