Questions about running my sulfuric stripping cell

[resabed01]

Just the other day I set up my first stripping cell so I can start stripping the gold off of the 10Kg of gold plated costume jewelry I've accumulated. Many thanks to this website and Steve's videos for all the help getting me started.
I'm using sulfuric acid that I've concentrated from battery acid on a hot plate. I estimate it to be somewhere around 90%. First, what purpose does the glycerine serve?
Also I noticed when I'm stripping an article, when first dipped into the acid it reacts like it should. The color quickly shifts from gold to silver and as the stripping continues the color then slowly shifts from silver to copper.
When the color changed from gold to silver is the cell done stripping the gold? What layer(s) resides below the gold but above the copper? I'm not sure but is this nickel? Zinc?
Reason I'm asking is because the cell looks to be collecting gray mud not black and the acid is becoming tinted blue. Maybe I'm leaving the piece in too long by stripping down to copper?
Thanks

 

[Harold_V]

First, what purpose does the glycerine serve?

It serves no purpose, and is not required.

Also I noticed when I'm stripping an article, when first dipped into the acid it reacts like it should. The color quickly shifts from gold to silver and as the stripping continues the color then slowly shifts from silver to copper.

When the gold color is gone, so, too, is the gold. That's an excellent time to pull out the material. What I'd recommend is that if you do them in bulk, that they be dumped, reloaded, then stripped briefly once again, to ensure that any traces that may have been protected by contact with other pieces will now be stripped. Any further action results in pulling base metals. No harm, just more garbage for you to deal with when you turn to refining the resulting slimes.

When the color changed from gold to silver is the cell done stripping the gold?

Yep! And I think you'll find that costume jewelry has very little on it in the way of gold. Just enough to color the piece, which is why it changes color so quickly. It's almost not worth the trouble to strip.

What layer(s) resides below the gold but above the copper? I'm not sure but is this nickel? Zinc?

Nickel has been used as a barrier. It prevents migration of the gold towards the base metal. As thin as the gold is applied, it would take but a very short period of time for the gold to be absorbed by the base metal. Migration of gold is a well documented phenomenon.

Reason I'm asking is because the cell looks to be collecting gray mud not black and the acid is becoming tinted blue. Maybe I'm leaving the piece in too long by stripping down to copper?
Thanks

That would be my impression.

Harold

 

[resabed01]

Hi Harold,

Thanks for the reply. It's all starting to make sense now that I've had the chance to do a bit of stripping in the cell. Reading all day about it is one thing, doing it and experiencing it is another. I learn by doing.
I suspected the gold layer was very thin on some pieces. Now that I know I don't need to strip down to the copper layer it will save me time and reduce the slimes.
I do notice a difference in gold thicknesses between pieces. Also I do notice a difference in the intermediate plating layers on some pieces.
I stripped a gold plated spoon that was marked 24 KARAT GOLD PLATED JAPAN and once the gold layer went the cell spent much time chewing on a dull gray metal which I didn't think was nickel.
Since this is my first attempt at the cell I thought I'd keep it simple and small. I'm running it in a pyrex dish with about 600ml of electrolyte. There is nothing uniform about costume jewelry. Some pieces have a lot of surface area and are perfectly suited to my current cell. Chains are a whole other matter. When a chain is dipped into the electrolyte, the acid get between the links and stops the current flow effectively stopping the stripping process. Once I work through the larger pieces I will have to run batches for the small items and chains. I also have a some gold filled chains I will have to separate out from the batch and run separately.

It will be interesting to see my yield once I work through this batch. I've read the yield will be quite low so I don't have my expectations set high.